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- Front Matter: Volume 9144
- Ultraviolet Instruments and Missions I
- Ultraviolet Instruments and Missions II
- Solar Instruments
- Gamma-ray Telescopes, Optics and Instruments
- Gamma-ray Sky Surveys II
- Polarimetry Missions
- Fifteen Years of Chandra and XMM/Newton: Lessons Learned
- Future Directions in UV to Gamma-ray Space Astronomy and Perspectives from Agencies
- Cosmic Ray Measurements in Space
- Detectors for High-energy Astrophysics
- X-ray Optics I
- X-ray Optics II
- Instrumentation for Polarimetry
- MAXI and NuStar
- Future Missions I: Astrosat and Spektrum-Roentgen Gamma
- Future Missions II: Neutron Stars to Gamma-ray Bursts
- Future Missions III: ASTRO-H
- The Next Generation: Athena I
- The Next Generation: Athena II
- The Next Generation: Small Mission Concepts
- The Next Generation: LOFT
- Poster Session
Front Matter: Volume 9144
Front Matter: Volume 9144
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This PDF file contains the front matter associated with SPIE Proceedings Volume 9144, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.
Ultraviolet Instruments and Missions I
Instrumentation of the WSO-UV project
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Dedicated to spectroscopic and imaging observations of the ultraviolet sky, the World Space Observatory - Ultraviolet mission is a Russian-Spanish collaboration. The project consists of a 1.7m telescope with instrumentation able to perform: a) high resolution (R ≥50 000) spectroscopy by means of two echellé spectrographs covering the 115–310 nm spectral range; b) long slit (1x75 arcsec) low resolution (R ∼ 1000) spectroscopy with a near-UV channel and a far-UV channel to cover the 115–305 nm spectral range; c) near-UV and a far-UV imaging channels covering the 115-320 nm wavelength range; d) slitless spectroscopy with spectral resolution of about 500 in the full 115–320 nm spectral range. Here we present the WSO-UV focal plane instruments, their status of implementation, and the expected performances.
Update on the CASTOR mission concept: scientific opportunities in the Euclid and WFIRST era
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CASTOR (the Cosmological Advanced Survey Telescope for Optical and uv Research) is a proposed CSA-led mission that would carry out deep, high-resolution imaging at ultraviolet and blue-optical wavelengths. Operating close to the diffraction limit, the 1m CASTOR telescope would have a spatial resolution comparable to the Hubble Space Telescope (HST), but with an instantaneous field of view of 1.2° x 0.6° -- about two hundred times larger than that of the Advanced Camera for Surveys on HST. Imaging would be carried out simultaneously in three non-overlapping bandpasses: UV (0.15-0.3 μm), u′ (0.3-0.4 μm) and g (0.4-0.55 μm). In the blue-optical region, CASTOR imaging would far exceed that from LSST in terms of depth and angular resolution, even after a decade of LSST operations. In this review, we summarize the various technical efforts being carried out in support of the CASTOR mission concept, and describe the potential scientific synergy between the CASTOR, Euclid and WFIRST missions.
Improved resolution in wide-field ultraviolet astronomical imaging
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Heritage wide-field ultraviolet imagers have observed large (~30°) fields-of-view, but suffer from relatively poor (~0.6°) spatial resolution. Improvements in mirror design and fabrication technology allow for a new two-mirror design that preserves a large (40°x20°) field-of-view, while improving spatial resolution by nearly a factor of ten to 0.07° while imaging onto a flat focal surface. Such an imager has uses in a number of ultraviolet astronomical applications, including plasmaspheric imaging and monitoring of the interplanetary medium.
SubLymE: the sub-Lyman alpha explorer
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The Sub-Lyman α Explorer (SubLymE) will be proposed to NASA as a Small Explorer mission in response to the anticipated Announcement of Opportunity in fall 2014. It will provide multi-color imaging in the 102 – 120 nm spectral window with 2 arc second resolution and a field of view 12 arc minutes in diameter. No astronomical imaging has been done in this bandpass previously. SubLymE will enable a host of previously impossible astronomical observations but its optical design and operational planning have been optimized around two key projects. 1: The mission will perform a survey of local galaxies, identifying and characterizing the youngest and most massive stellar clusters in local star-forming and star-bursting galaxies. These stellar clusters drive the physical and chemical evolution of galaxies like the Milky Way. 2: SubLymE will directly measure the amount and spatial distribution of ionizing photon escape from star-forming galaxies in the local universe (0.22 < z < 0.5), a critical measurement for understanding how the intergalactic medium was ionized during the epoch of reionization. We present the current optical design and predicted performance for SubLymE, and summarize its primary science objectives.
Ultraviolet Instruments and Missions II
The assembly, calibration, and preliminary results from the Colorado high-resolution Echelle stellar spectrograph (CHESS)
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The Colorado High-resolution Echelle Stellar Spectrograph (CHESS) is a far ultraviolet (FUV) rocket-borne experiment designed to study the atomic-to-molecular transitions within translucent interstellar clouds. CHESS is an objective echelle spectrograph operating at f/12.4 and resolving power of 120,000 over a band pass of 100 – 160 nm. The echelle flight grating is the product of a research and development project with LightSmyth Inc. and was coated at Goddard Space Flight Center (GSFC) with Al+LiF. It has an empirically-determined groove density of 71.67 grooves/mm. At the Center for Astrophysics and Space Astronomy (CASA) at the University of Colorado (CU), we measured the efficiencies of the peak and adjacent dispersion orders throughout the 90 – 165 nm band pass to characterize the behavior of the grating for pre-flight calibrations and to assess the scattered-light behavior. The crossdispersing grating, developed and ruled by Horiba Jobin-Yvon, is a holographically-ruled, low line density (351 grooves/mm), powered optic with a toroidal surface curvature. The CHESS cross-disperser was also coated at GSFC; Cr+Al+LiF was deposited to enhance far-UV efficiency. Results from final efficiency and reflectivity measurements of both optics are presented. We utilize a cross-strip anode microchannel plate (MCP) detector built by Sensor Sciences to achieve high resolution (25 μm spatial resolution) and data collection rates (~ 106 photons/second) over a large format (40mm round, digitized to 8k x 8k) for the first time in an astronomical sounding rocket flight. The CHESS instrument was successfully launched from White Sands Missile Range on 24 May 2014. We present pre-flight sensitivity, effective area calculations, lab spectra and calibration results, and touch on first results and post-flight calibration plans.
The UVIT telescopes on board the ISRO Astrosat Observatory
J. B. Hutchings
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UVIT consists of two co-aligned 38cm telescopes that provide ~1 arsec resolution imaging over 28 arcmin fields, in FUV, NUV, and Visible bands simultaneously. Each channel has a choice of filters, and, for the UV channels, gratings. UVIT is also co-aligned with three X-ray telescopes on the observatory, and all operate together. This paper gives details of the operation and performance of the instrument.
Solar Instruments
The extreme UV imager of solar orbiter: from detailed design to flight model
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The Extreme Ultraviolet Imager (EUI) on-board the Solar Orbiter mission will provide full-sun and high-resolution image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum ultraviolet. After the breadboarding and prototyping activities that focused on key technologies, the EUI project has completed the design phase and has started the final manufacturing of the instrument and its validation. The EUI instrument has successfully passed its Critical Design Review (CDR). The process validated the detailed design of the Optical Bench unit and of its sub-units (entrance baffles, doors, mirrors, camera, and filter wheel mechanisms), and of the Electronic Box unit. In the same timeframe, the Structural and Thermal Model (STM) test campaign of the two units have been achieved, and allowed to correlate the associated mathematical models. The lessons learned from STM and the detailed design served as input to release the manufacturing of the Qualification Model (QM) and of the Flight Model (FM). The QM will serve to qualify the instrument units and sub-units, in advance of the FM acceptance tests and final on-ground calibration.
In-flight UV and polarized-VL radiometric calibrations of the solar orbiter/METIS imaging coronagraph
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METIS is an innovative inverted occulted solar coronagraph capable of obtaining for the first time simultaneous imaging of the full corona in linearly polarized visible-light (580-640 nm) and narrow-band (± 10 nm) ultraviolet H I Ly-α (121.6 nm). It has been selected to fly aboard the Solar Orbiter1 spacecraft, whose launch is foreseen in July 2017. Thanks to its own capabilities and exploiting the peculiar opportunities offered by the Solar Orbiter planned orbit, METIS will address some of the still open issues in understanding the physical processes in the corona and inner heliosphere. The Solar Orbiter Nominal Mission Phase (NMP) will be characterized by three scientific observing windows per orbit and METIS will perform at least one in-flight calibration per observing window. The two imaging channels of METIS will be calibrated on ground and periodically checked, verified and re-calibrated in-flight. In particular, radiometric calibration images will be needed to determine the absolute brightness of the solar corona. For UV radiometric calibration a set of targets is represented by continuum-emitting early type bright stars (e.g. A and B spectral types) whose photospheres produce a bright far-ultraviolet continuum spectrum stable over long timescales. These stars represent an important reference standard not only for METIS in-flight calibrations but also for other Solar Orbiter instruments and they will be crucial for instruments cross-calibrations as well. For VL radiometric calibration, a set of linearly polarized stars will be used. These targets shall have a minimum degree of linear polarization (DoLP > 5%) and a detectable magnitude, compatible with the instrument integration times constrained by the desired S/N ratio and the characteristics of the spacecraft orbit dynamics.
Gamma-ray Telescopes, Optics and Instruments
The Gamma Cube: a novel concept of gamma-ray telescope
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There is a large gap in between the Integral and Fermi spectral domains that is unobserved since the end of the CGRO mission and its Comptel experiment. There were many attempts to fill this gap but no proposal succeeded yet to convince a space agency to plan a mission. There are many reasons contributing to this situation but the most important one is that neither mirrors nor present particle tracking devices are effective at these energies. We propose here a novel design allowing particle tracking for a gamma-ray telescope in the 5–100 MeV band. The idea of this experiment is to image the ionizing tracks of charged particles using the light produced in a scintillator. The experiment operates as a pair creation telescope at high energy and as a Compton telescope with electron tracking at low energy. The telescope features a large scintillator transparent to the produced scintillation light, an ad-hoc optical system and a high resolution and highly sensitive imager. We review the requirements for each of these sub-systems and propose an experiment design taking into account the space constraints. We emphasize the numerous conceptual advantages of such a system as well as the identified difficulties.
Scientific motivations and technical design considerations for future high-energy gamma-ray telescopes in light of lessons learned from the Fermi Large Area Telescope
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Five years into the Fermi Gamma-ray Space Telescope (Fermi) mission we have learned a great deal about the γ-ray sky, yet many open questions remain, and many new puzzles have arisen. In this contribution we will consider the science drivers for a variety of topics in high-energy gamma-ray astronomy, and how these drivers map into design considerations for future gamma-ray instruments in the energy range above 5 MeV. Specifically, we take the performance parameters and data set of the Large Area Telescope on the Fermi observatory (Fermi-LAT) as a baseline, and consider the scientific questions that could be probed by improving those parameters. We will also discuss the current state of detector technologies used in space-based γ-ray telescopes and discuss the magnitude of advances that would be required to make a future Fermi-like mission transformational enough to warrant the cost and effort. These summaries are intended to be useful for selecting technologies and making basic design decisions for future γ-ray telescopes.
PANGU: A high resolution gamma-ray space telescope
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We describe the instrument concept of a high angular resolution telescope dedicated to the sub-GeV (from ≥10 MeV to ≥1 GeV) gamma-ray photon detection. This mission, named PANGU (PAir-productioN Gamma-ray Unit), has been suggested as a candidate for the joint small mission between the European Space Agency (ESA) and the Chinese Academy of Science (CAS). A wide range of topics of both astronomy and fundamental physics can be attacked with PANGU, covering Galactic and extragalactic cosmic-ray physics, extreme physics of a variety of extended (e.g. supernova remnants, galaxies, galaxy clusters) and compact (e.g. black holes, pulsars, gamma-ray bursts) objects, solar and terrestrial gamma-ray phenomena, and searching for dark matter decay and/or annihilation signature etc. The unprecedented point spread function can be achieved with a pair-production telescope with a large number of thin active tracking layers to precisely reconstruct the pair-produced electron and positron tracks. Scintillating fibers or thin silicon micro-strip detectors are suitable technology for such a tracker. The energy measurement is achieved by measuring the momentum of the electrons and positrons through a magnetic field. The innovated spectrometer approach provides superior photon pointing resolution, and is particular suitable in the sub-GeV range. The level of tracking precision makes it possible to measure the polarization of gamma rays, which would open up a new frontier in gamma-ray astronomy. The frequent full-sky survey at sub-GeV with PANGU's large field of view and significantly improved point spread function would provide crucial information to GeV-TeV astrophysics for current/future missions including Fermi, DAMPE, HERD, and CTA, and other multi-wavelength telescopes.
MeV gamma-ray Compton camera using a gaseous electron tracker for background-suppressed observation
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As a next generation MeV gamma-ray telescope, we develop an electron-tracking Compton camera (ETCC) that consists of a gaseous electron tracker surrounded by pixel scintillator arrays. The tracks of the Compton-recoil electron measured by the tracker restrict the incident gamma-ray direction to an arc region on the sky and reject background by using the energy loss rate dE/dx and a Compton-kinematics test. In 2013, we constructed, for a balloon experiment, a 30-cm-cubic ETCC with an effective area of ~1 cm2 for detecting sub-MeV gamma rays (5 σ detection of the Crab Nebula for 4 h). In future work, we will extend this ETCC to an effective area of ~10 cm2. In the present paper, we report the performance of the current ETCC.
Gamma-ray Sky Surveys II
All-sky Compton imager
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The All-Sky Compton Imager (ASCI) is a mission concept for MeV Gamma-Ray astronomy. It consists of a compact array of cross-strip germanium detectors, shielded only by a plastic anticoicidence, and weighting less than 100 kg. Situated on a deployable structure at a distance of 10 m from the spacecraft orbiting at L2 or in a HEO, the ASCI not only avoids albedo- and spacecraft-induced background, but it benefits from a continuous all-sky exposure. The modest effective area is more than compensated by the 4 π field-of-view. Despite its small size, ASCI's γ-ray line sensitivity after its nominal lifetime of 3 years is ~ 10-6 ph cm-2 s-1 at 1 MeV for every γ-ray source in the sky. With its high spectral and 3-D spatial resolution, the ASCI will perform sensitive γray spectroscopy and polarimetry in the energy band 100 keV-10 MeV. The All-Sky Compton Imager is particularly well suited to the task of measuring the Cosmic Gamma-Ray Background – and simultaneously covering the wide range of science topics in gamma-ray astronomy.
PACT: a sensitive 100 keV-10 MeV all sky pairs and Compton telescope
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PACT is a Pair And Compton Telescope that aims to make a sensitive survey of the gamma-ray sky between 100 keV and 100 MeV. It will be devoted to the detection of radioactivity lines from present and past supernova explosions, the observation of thousands of new blazars, and the study of polarized radiations from gamma-ray bursts, pulsars and accreting black holes. It will reach a sensitivity of one to two orders of magnitude lower than COMPTEL/CGRO (e.g. about 50 times lower for the broad-band, survey sensitivity at 1 MeV after 5 years). The concept of PACT will be proposed for the AstroMeV mission in the framework of the M4 ESA Call. It is based upon three main components: a silicon-based gamma-ray tracker, a crystal-based calorimeter (e.g. CeBr3:Sr), and an anticoincidence detector made of plastic scintillator panels. Prototypes of these detector planes are currently tested in the laboratories.
Sub-MeV all sky survey with a compact Si/CdTe Compton telescope
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Recent progress in wide field of view or all-sky observations such as Swift/BAT hard X-ray monitor and Fermi GeV gamma-ray observatory has opened up a new era of time-domain high energy astro-physics addressing new insight in, e.g., particle acceleration in the universe. MeV coverage with comparable sensitivity, i.e. 1 ~ 10 mCrab is missing and a new MeV all-sky observatory is needed. These new MeV mission tend to be large, power- consuming and hence expensive, and its realization is yet to come. A compact sub-MeV (0.2-2 MeV) all-sky mission is proposed as a path finder for such mission. It is based on a Si/CdTe semiconductor Compton telescope technology employed in the soft gamma-ray detector onboard ASTRO-H, to be launched in to orbit on late 2015. The mission is kept as small as 0:5 X 0:5 X 0:4 m3, 150 kg in weight and 200 W in power in place of the band coverage above a few MeV, in favor of early realization as a sub-payload to other large platforms, such as the international space station.
Polarimetry Missions
X-ray gamma-ray polarimetry small satellite PolariS
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PolariS (Polarimetry Satellite) is a Japanese small satellite mission dedicated to polarimetry of X-ray and γ-ray sources. The primary aim of the mission is to perform hard X-ray (10-80 keV) polarimetry of sources brighter than 10 mCrab. For this purpose, PolariS employs three hard X-ray telescopes and scattering type imaging polarimeters. PolariS will measure the X-ray polarization for tens of sources including extragalactic ones mostly for the first time. The second purpose of the mission is γ-ray polarimetry of transient sources, such as γ-ray bursts (GRBs). Wide field polarimeters based on similar concept as that used in the IKAROS/GAP but with higher sensitivity will be used, and polarization measurement of 10 GRBs per year is expected.
Pre-flight performance of a micro-satellite TSUBAME for X-ray polarimetry of gamma-ray bursts
Yoichi Yatsu,
Kei Ito,
Shin Kurita,
et al.
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To measure the polarization of gamma-ray bursts in X-ray energy band, we have developed a 50 kg micro-satellite named "SUBAME". The satellite has a compact and high-sensitive hard X-ray polarimeter employing newly-developed shock resistant multi-anode photomultipliers and Si avalanche photodiodes. Thanks to the ultra low-noise detectors and signal processors, the polarimeter can cover a wide energy range of 30200 keV even at 25°C with a high modulation factor of 62 %. TSUBAME is in the phase of final functional tests waiting for shipping to Baikonur and will be launched into a sun-synchronous orbit at an altitude of 700 km in late 2014. In this paper, the pre-ight performance of the gamma-ray detector system and the satellite bus system are presented.
The POLAR gamma-ray burst polarimeter onboard the Chinese Spacelab
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POLAR is a joint European-Chinese experiment aimed at a precise measurement of hard X-ray polarization (50-500 keV) of the prompt emission of Gamma-Ray Bursts. The main aim is a better understanding of the geometry of astrophysical sources and of the X-ray emission mechanisms. POLAR is a compact Compton polarimeter characterized by a large modulation factor, effective area, and field of view. It consists of 1600 low-Z plastic scintillator bars read out by 25 at-panel multi-anode photomultipliers. The incoming X-rays undergo Compton scattering in the bars and produce a modulation pattern; experiments with polarized synchrotron radiation and GEANT4 Monte Carlo simulations have shown that the polarization degree and angle can be retrieved from this pattern with the accuracy necessary for identifying the GRB mechanism. The flight model of POLAR is currently under construction in Geneva. The POLAR instrument will be placed onboard the Chinese spacelab TG-2, scheduled for launch in low Earth orbit in 2015. The main milestones of the space qualification campaign will be described in the paper.
X-ray polarization capabilities of a small explorer mission
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X-ray polarization measurements hold great promise for studying the geometry and emission mechanisms in the strong gravitational and magnetic fields that surround black holes and neutron stars. In spite of this, the observational situation remains very limited; the last instrument dedicated to X-ray polarimetry flew decades ago on OSO-8, and the few recent measurements have been made by instruments optimized for other purposes. However, the technical capabilities to greatly advance the observational situation are in hand. Recent developments in micro-pattern gas detectors allow use of the polarization sensitivity of the photo-electric effect, which is the dominant interaction in the band above 2 keV. We present the scientific and technical requirements for an X-ray polarization observatory consistent with the scope of a NASA Small Explorer (SMEX) mission, along with a representative catalog of what the observational capabilities and expected sensitivities for the first year of operation could be. The mission is based on the technically robust design of the Gravity and Extreme Magnetism SMEX (GEMS) which completed a Phase B study and Preliminary Design Review in 2012. The GEMS mission is enabled by time projection detectors sensitive to the photo-electric effect. Prototype detectors have been designed, and provide engineering and performance data which support the mission design. The detectors are further characterized by low background, modest spectral resolution, and sub-millisecond timing resolution. The mission also incorporates high efficiency grazing incidence X-ray mirrors, design features that reduce systematic errors (identical telescopes at different azimuthal angles with respect to the look axis, and mounted on a rotating spacecraft platform), and a moderate capability to perform Target of Opportunity observations. The mission operates autonomously in a low earth, low inclination orbit with one to ten downlinks per day and one or more uplinks per week. Data and calibration products will be made available through the High Energy Astrophysics Science and Archival Research Center (HEASARC).
POET: a SMEX mission for gamma ray burst polarimetry
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Polarimeters for Energetic Transients (POET) is a mission concept designed to t within the envelope of a NASA Small Explorer (SMEX) mission. POET will use X-ray and gamma-ray polarimetry to uncover the energy release mechanism associated with the formation of stellar-mass black holes and investigate the physics of extreme magnetic ields in the vicinity of compact objects. Two wide-FoV, non-imaging polarimeters will provide polarization measurements over the broad energy range from about 2 keV up to about 500 keV. A Compton scatter polarimeter, using an array of independent scintillation detector elements, will be used to collect data from 50 keV up to 500 keV. At low energies (2{15 keV), data will be provided by a photoelectric polarimeter based on the use of a Time Projection Chamber for photoelectron tracking. During a two-year baseline mission, POET will be able to collect data that will allow us to distinguish between three basic models for the inner jet of gamma-ray bursts.
Fifteen Years of Chandra and XMM/Newton: Lessons Learned
Fifteen years of Chandra operation: scientific highlights and lessons learned
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NASA's Chandra X-Ray Observatory, designed for three years of operation with a goal of five years, is now entering its 15-th year of operation. Thanks to its superb angular resolution, the Observatory continues to yield new and exciting results, many of which were totally unanticipated prior to launch. We discuss the current technical status, review some recent scientific highlights, indicate a few future directions, and present what we are the most important lessons learned from our experience of building and operating this great observatory.
Lessons we learned designing and building the Chandra telescope
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2014 marks the crystal (15th) anniversary of the launch of the Chandra X-ray Observatory, which began its existence as the Advanced X-ray Astrophysics Facility (AXAF). This paper offers some of the major lessons learned by some of the key members of the Chandra Telescope team. We offer some of the lessons gleaned from our experiences developing, designing, building and testing the telescope and its subsystems, with 15 years of hindsight. Among the topics to be discussed are the early developmental tests, known as VETA-I and VETA-II, requirements derivation, the impact of late requirements and reflection on the conservatism in the design process.
Fifteen years of experience with the Reflection Grating Spectrometer on XMM-Newton
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The RGS instrument is the X–ray spectrometer on board the XMM-Newton satellite, launched December 1999, and still fully operational. It consists of a reflection grating to disperse the incoming X–rays and a CCD camera as detector. In the past fifteen years a lot of experience has been gained in operating and calibrating this instrument. In this presentation we report on the calibration methods and status, new instrumental modes and detector performance, which were acquired and developed based on the in-flight experiences with the instrument. Selecting the proper operating modes, combined with careful data processing based on target characteristics and science goals, allows detection of weak spectral features, despite slowly degrading detectors due to radiation damage and contamination. At present the instrument has excellent health status and performance, and will be one of the few major instruments for X–ray spectroscopy in the coming years, until supplemented by new missions like ASTRO-H and, in particular, Athena.
Lessons from the development and operation of the Chandra x-ray observatory
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Genuine teamwork was a key ingredient of the success of the Chandra x-ray observatory mission. Examples are the science center personnel working as part of the instrument principal investigators (IPI) teams during pre-launch development, the Smithsonian Astrophysical Observatory (SAO) supporting NASA/Marshall Space Flight Center (MSFC) by directly working with the prime contractor, TRW (now Northrop Grumman Aerospace Systems), and TRW acceptance of outside scientists performing the data reduction and analysis for qualification of the aspect camera. An end-to-end thread was defined early on, based on the MSFC/SAO operation of the Einstein observatory x-ray telescope, and covered the cycle from solicitation and peer review of observation proposals through scheduling to data processing and delivery. An open science working group chaired by MSFC included instrument principal investigators and interdisciplinary scientists spanning diverse astrophysical and instrumental expertise.
Future Directions in UV to Gamma-ray Space Astronomy and Perspectives from Agencies
Space astronomy and astrophysics program by NASA
Paul L. Hertz
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The National Aeronautics and Space Administration recently released the NASA Strategic Plan 20141, and the NASA Science Mission Directorate released the NASA 2014 Science Plan3. These strategic documents establish NASA’s astrophysics strategic objectives to be (i) to discover how the universe works, (ii) to explore how it began and evolved, and (iii) to search for life on planets around other stars. The multidisciplinary nature of astrophysics makes it imperative to strive for a balanced science and technology portfolio, both in terms of science goals addressed and in missions to address these goals. NASA uses the prioritized recommendations and decision rules of the National Research Council’s 2010 decadal survey in astronomy and astrophysics2 to set the priorities for its investments. The NASA Astrophysics Division has laid out its strategy for advancing the priorities of the decadal survey in its Astrophysics 2012 Implementation Plan4. With substantial input from the astrophysics community, the NASA Advisory Council’s Astrophysics Subcommittee has developed an astrophysics visionary roadmap, Enduring Quests, Daring Visions5, to examine possible longer-term futures. The successful development of the James Webb Space Telescope leading to a 2018 launch is an Agency priority. One important goal of the Astrophysics Division is to begin a strategic mission, subject to the availability of funds, which follows from the 2010 decadal survey and is launched after the James Webb Space Telescope. NASA is studying a Wide Field Infrared Survey Telescope as its next large astrophysics mission. NASA is also planning to partner with other space agencies on their missions as well as increase the cadence of smaller Principal Investigator led, competitively selected Astrophysics Explorers missions.
Space astronomy and astrophysics program by CSA
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Canada became actively engaged in space astronomy in the 1990s by contributing two fine guidance sensors to the FUSE Far-UV mission (NASA 1999-2008). In the same period, Canada contributed to ODIN’s infrared instrument (ESA 2001-2006) and correlators for VSOP (JAXA 1997-2005). In early 2000, Canada developed its own space telescope, Micro-variability and Observations of STars (MOST), a 15-cm telescope on a microsatellite, operating since 2003, and more recently contributed to the realization of the BRITE nanosatellites constellation. Canada also provided hardware to the European Space Agency’s Herschel HIFI instrument and simulators to the SPIRE instrument and data analysis tools for Planck. More recently the Canadian Space Agency (CSA) delivered detector units for the UVIT instrument on board the Indian Space Research Organisation’s (ISRO) ASTROSAT. The CSA’s most important contribution to a space astronomy mission to date is the Fine Guidance Senor (FGS) and Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument to NASA’s James Webb Space Telescope. The CSA is currently building the laser metrology system for JAXA’s ASTRO-H hard X-ray telescope. Canadian astronomers contributed to several high profile stratospheric balloon projects investigating the CMB and the CSA recently established a balloon launch facility. As expressed in Canada’s new Space Policy Framework announced in February 2014, Canada remains committed to future space exploration endeavors. The policy aims at ensure that Canada is a sought-after partner in the international space exploration missions that serve Canada’s national interests; and continuing to invest in the development of Canadian contributions in the form of advanced systems and optical instruments. In the longer term, through consultations and in keeping the Canadian astronomical community’s proposed Long Range Plan, the CSA is exploring possibilities to contributions to important missions such as WFIRST, SPICA and Athena and in other areas, by initiating concept and pre-mission studies and enabling technology developments. These reflect the following scientific priorities identified: dark energy and the accelerating universe, addressed by large survey missions; high-energy astrophysics, which includes UV and X-ray missions; and the understanding of star formation and proto-planetary systems and to begin characterizing exoplanets, mainly by infra-red space observatories.
Cosmic Ray Measurements in Space
The high energy cosmic-radiation detection (HERD) facility onboard China's Space Station
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The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads of the cosmic lighthouse program onboard China's Space Station, which is planned for operation starting around 2020 for about 10 years. The main scientific objectives of HERD are indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is composed of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 104 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. The top STK microstrips of seven X-Y layers are sandwiched with tungsten converters to make precise directional measurements of incoming electrons and gamma-rays. In the baseline design, each of the four side SKTs is made of only three layers microstrips. All STKs will also be used for measuring the charge and incoming directions of cosmic rays, as well as identifying back scattered tracks. With this design, HERD can achieve the following performance: energy resolution of 1% for electrons and gamma-rays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10-5; effective geometrical factors of >3 m2sr for electron and diffuse gamma-rays, >2 m2sr for cosmic ray nuclei. R and D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD and the prototype of one layer of CALO.
Detectors for High-energy Astrophysics
Large high impedance silicon micro-calorimeters for x-rays camera: status and perspectives
J. L. Sauvageot,
C. Pigot,
X. de la Broïse,
et al.
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In this paper, we present our developments on micro-calorimeter arrays, based on High Impedance Silicon sensors (MIS or resistive TES) micro-calorimeters and GaAS-GaAlAs HEMTs / SiGe cryo-electronics, started 5 years ago. We show the pixel design, the main steps to build a 32x32 array. We are presently developing two kinds of high impedance sensors: Metal-Insulator-Sensors and High Resistivity Transition Edge Sensors. We described our associated FrontEnd electronics and detailed system level analysis of the foreseen camera. We discuss why we will be able to handle a camera with a large number of pixels (thanks to excellent thermal insulation and no electronic power consuming at the 50mK stage). We discuss the main technological building blocks (Absorber, Sensor) and their present status.
Development of DEPFET active pixel sensors to improve the spectroscopic response for high time resolution applications
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The WFI instrument of ATHENA will provide large field of view in combination with high count-rate capability to address key questions of modern astrophysics. It will utilize a DEPFET based active pixel sensor as focal plane detector. To achieve fastest timings, these sensors can be operated by addressing a region of interest. While this window mode operation enhances time resolution, the probability to collect events during signal processing will become non negligible. Due to the incomplete signal evaluation, these so called misfit events cause an additional background contribution, which will be dominant at very fast timings as required for ATHENA. To sustain the spectral performance a built-in electronic shutter and an intermediate storage can be implemented into each pixel. While the shutter is capable to effectively suppress misfit collection and thus maintains the spectral performance, the implementation of a storage region diminishes possible dead times and improves throughput. We will present measurements on prototype devices demonstrating the benefit of a fast built-in shutter for DEPFET devices operated at high frame rates. Furthermore we will show results of first measurements on structures that combine a built-in shutter with an intermediate storage, obviating dead times and simultaneously improving the spectral response.
Development and performance of Kyoto's x-ray astronomical SOI pixel (SOIPIX) sensor
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We have been developing monolithic active pixel sensors, known as Kyoto’s X-ray SOIPIXs, based on the CMOS SOI (silicon-on-insulator) technology for next-generation X-ray astronomy satellites. The event trigger output function implemented in each pixel offers microsecond time resolution and enables reduction of the non-X-ray background that dominates the high X-ray energy band above 5–10 keV. A fully depleted SOI with a thick depletion layer and back illumination offers wide band coverage of 0.3–40 keV. Here, we report recent progress in the X-ray SOIPIX development. In this study, we achieved an energy resolution of 300 eV (FWHM) at 6 keV and a read-out noise of 33 e- (rms) in the frame readout mode, which allows us to clearly resolve Mn-Kα and Kβ. Moreover, we produced a fully depleted layer with a thickness of 500 μm. The event-driven readout mode has already been successfully demonstrated.
ART-XC/SRG: status of the x-ray focal plane detector development
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The Russian Space Research Institute (IKI) has developed CdTe detectors for the focal plane of the ART-XC/SRG instrument. The CdTe crystal has dimensions about 30 × 30 × 1 mm. Top and bottom sides of the detector each contain 48 strips and a guard ring. The ASIC VA64TA1 is connected to the CdTe crystal by AC-coupling for both DSSD sides. This approach allows one to have the same ground level for both electronic parts and to operate detectors with different leakage currents without reconfiguration of the VA64TA1 chips. One CdTe crystal and two ASICs are integrated with thermal sensors and Peltier cooler in a big hybrid integrated circuit. This detector is hermetically sealed by a cover with beryllium window. For ground testing the detector volume is filled with dry nitrogen. Peltier cooler is used during ground tests only. Together with the hermetic case package it allows us to operate the detector at low temperature during all ART-XC telescope development tests. When in space, the detector cooling will be provided by a radiator and heat pipes. Polarization rate temperature and voltage dependences as well as splitting charges between electrodes are being studied. IKI manufactured dozen X-ray cameras with detectors and supporting electronics for EM, QM and flight model of the ART-XC telescope. Spectroscopic and imaging performances of the detectors were tested on the IKI’s X-Ray Calibration Facility. Current status of the focal plane detector development and testing will be presented.
Scintillators with silicon photomultiplier readouts for high-energy astrophysics and heliophysics
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Space-based gamma-ray and neutron detectors face strict constraints of mass, volume, and power, and must endure harsh operating environments. Scintillator materials have a long history of successful operation under these conditions, and new materials offer greatly improved performance in terms of efficiency, time response, and energy resolution. The use of scintillators in space remains constrained, however, by the mass, volume, and fragility of the associated light readout device, typically a vacuum photomultiplier tube (PMT). Recently developed silicon photomultipliers (SiPMs) offer gains and efficiencies similar to those of PMTs, but with greatly reduced mass and volume, high ruggedness, and no high-voltage requirements. We have therefore been investigating the use of SiPM readouts for scintillator gamma-ray and neutron detectors, with an emphasis on their suitability for space-based instruments for astrophysics and heliophysics. We present preliminary radiation hardness tests of two promising SiPM devices, and describe two concepts for SiPM-based instruments: an advanced scintillator-based Compton telescope, and a double-scatter neutron telescope suitable for measuring fast solar and magnetospheric neutrons. Supporting laboratory measurements are presented to demonstrate the feasibility of these telescope concepts.
X-ray Optics I
Affordable and lightweight high-resolution x-ray optics for astronomical missions
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Future x-ray astronomical missions require x-ray mirror assemblies that provide both high angular resolution and large photon collecting area. In addition, as x-ray astronomy undertakes more sensitive sky surveys, a large field of view is becoming increasingly important as well. Since implementation of these requirements must be carried out in broad political and economical contexts, any technology that meets these performance requirements must also be financially affordable and can be implemented on a reasonable schedule. In this paper we report on progress of an x-ray optics development program that has been designed to address all of these requirements. The program adopts the segmented optical design, thereby is capable of making both small and large mirror assemblies for missions of any size. This program has five technical elements: (1) fabrication of mirror substrates, (2) coating, (3) alignment, (4) bonding, and (5) mirror module systems engineering and testing. In the past year we have made progress in each of these five areas, advancing the angular resolution of mirror modules from 10.8 arc-seconds half-power diameter reported (HPD) a year ago to 8.3 arc-seconds now. These mirror modules have been subjected to and passed all environmental tests, including vibration, acoustic, and thermal vacuum. As such this technology is ready for implementing a mission that requires a 10-arc-second mirror assembly. Further development in the next two years would make it ready for a mission requiring a 5-arc-second mirror assembly. We expect that, by the end of this decade, this technology would enable the x-ray astrophysical community to compete effectively for a major x-ray mission in the 2020s that would require one or more 1-arc-second mirror assemblies for imaging, spectroscopic, timing, and survey studies.
X-ray optical units made of glass: achievements and perspectives
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Future X-ray telescopes with very large collecting area, like the proposed Athena with more than 2 m2 effective area at 1 keV, need to be realized as assemblies of a large number of X-ray optical units, named X-ray Optical Units (XOUs). The Brera Astronomical Observatory (INAF-OAB) is developing a new technology to manufacture these modular elements, compatible with an angular resolution of 5 arcsec HEW (Half-Energy-Width). This technique consists in stacking in a Wolter-I configuration several layers of thin foils of glass, previously formed by direct hot slumping. The achievable global angular resolution of the optics relies on the required surface shape accuracy of slumped foils, on the smoothness of the mirror surfaces and on the correct integration and co-alignment of the mirror segments operated trough a dedicated Integration Machine (IMA). In this paper we provide an overview of the project development, reporting on the very promising results achieved so far, including in-focus full illumination X-ray tests of the prototype (Proof of Concept, POC#2, integrated at the beginning of 2013) for which an HEW of 22.1’’ has been measured at Panter/MPE. Moreover we report on the on-going activities, with a new integrated prototype (PoC#3). X-ray test in pencil beam revealed that at least a segment between two external ribs is characterized by an HEW well below 10’’. Lastly, the overall process up-grade to go from 20 m to 12m focal length (to be compatible with Athena+ configuration) is presented.
Optical design for a survey x-ray telescope
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Optical design trades are underway at the Goddard Space Flight Center to define a telescope for an x-ray survey mission. Top-level science objectives of the mission include the study of x-ray transients, surveying and long-term monitoring of compact objects in nearby galaxies, as well as both deep and wide-field x-ray surveys. In this paper we consider Wolter, Wolter-Schwarzschild, and modified Wolter-Schwarzschild telescope designs as basic building blocks for the tightly nested survey telescope. Design principles and dominating aberrations of individual telescopes and nested telescopes are discussed and we compare the off-axis optical performance at 1.0 KeV and 4.0 KeV across a 1.0 degree full field-of-view.
Next generation hard X-ray/soft gamma-ray optic design and implementation
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We discuss necessary improvements and further studies relevant to the design and eventual implementation of an accurately modeled multilayer coated X-ray optic operating in the hard X-ray/soft gamma-ray regime. The process improvements are substantiated through lessons learnt from NuSTAR.
Fabrication of large-area and low mass critical-angle x-ray transmission gratings
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Soft x-ray spectroscopy of celestial sources with high resolving power R = E/ΔE and large collecting area addresses important science listed in the Astro2010 Decadal Survey New Worlds New Horizons, such as the growth of the large scale structure of the universe and its interaction with active galactic nuclei, the kinematics of galactic outflows, as well as coronal emission from stars and other topics. Numerous studies have shown that a transmission grating spectrometer based on lightweight critical-angle transmission (CAT) gratings can deliver R = 3000-5000 and large collecting area with high efficiency and minimal resource requirements, providing spectroscopic figures of merit at least an order of magnitude better than grating spectrometers on Chandra and XMM-Newton, as well as future calorimeter-based missions. The recently developed CAT gratings combine the advantages of transmission gratings (low mass, relaxed figure and alignment tolerances) and blazed reflection gratings (high broad band diffraction efficiency, utilization of higher diffraction orders). Their working principle based on blazing through reflection off the smooth, ultra-high aspect ratio grating bar sidewalls has previously been demonstrated on small samples with x rays. For larger gratings (area greater than 1 inch square) we developed a fabrication process for grating membranes with a hierarchy of integrated low-obscuration supports. The fabrication involves a combination of advanced lithography and highly anisotropic dry and wet etching techniques. We report on the latest fabrication results of free-standing, large-area CAT gratings with polished sidewalls and preliminary x-ray tests.
X-ray Optics II
Progress on indirect glass slumping for future x-ray telescope optics
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Large X-ray telescopes for future observations need to combine a big collecting area with good angular resolution. Due to the mass limits of the launching rocket, light-weight materials are needed in order to enhance the collecting area in future telescopes. We study the development of mirror segments made from thin glass sheets which are shaped by thermal slumping. At MPE we follow the indirect approach which enables us the production of the parabolic and hyperbolic part of the Wolter type I mirrors in one piece. In our recent research we have used a test mould made of CeSiC™ for slumping processes in our lab furnace as well as in a heatable vacuum chamber, to avoid oxidation and air enclosure. Additional slumping tests in the vacuum furnace have been carried out using a Kovar mould and are compared with results under air. We describe the experimental set-up, the slumping process and the metrology methods and give an outlook on future activities.
Measuring the performance of adjustable x-ray optics with wavefront sensing
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Post-mounting figure correction is a promising avenue to produce low-mass, high-resolution X-ray telescopes. We have demonstrated the feasibility of this approach using piezoelectrically adjustable glass mirrors. Influence functions for various piezoelectric cells have previously been measured with an optical profilometer, but with significant noise. We have improved on both the speed and accuracy of these measurements using a Shack- Hartmann wavefront sensing system. Additionally, we have altered our wavefront sensing system to investigate the mid frequency roughness of our slumped glass mirrors. We report on initial results for measurements of both influence functions and mid frequency roughness and describe our path forward.
Development of the x-ray timing and polarization telescope optics
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X-ray Timing and Polarization (XTP) satellite, by using focusing optics and advanced detector technology, is dedicated to the study of Black Hole, Neutron Star, Quark Star and the physics under extreme gravity, density and magnetism. With a detection area of ~1 square meter and a combination of various types of X-ray telescopes, XTP is expected to make the most sensitive temporal and polarization observations with good energy resolution in 1-30 keV. We present a recent overview on segmented glass optics for XTP Telescope. This work is looking for improvement of the figure of the free-standing glass substrates, enhancement of quality of grazing incident depth-graded multilayers and a mounting technology for the substrates. We discuss metrology on glass figure, X-ray reflectivity and scatter of grazing incident depth-graded multilayers, and mounted structured optics. We also present plans for several prototype optics to be constructed in the upcoming year. Begin the abstract two lines below author names and addresses. The abstract summarizes key findings in the paper.
Miniature lightweight x-ray optics (MiXO) for solar system exploration
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Over the last few decades, grazing incidence X-ray optics have been a pivotal tool for advances in X-ray astronomy. They have been successfully employed in many great observatories such as ROSAT, Chandra X-ray Observatory and XMM-Newton. In planetary science, X-ray observations of Solar system objects are a great tool to understand the nature of the target bodies and the evolutionary history of the Solar system as a whole. To date, X-ray observations in near-target planetary missions have been limited to collimator-based instruments due to tight mass and volume constraints, arising from the multi-instrument nature of planetary missions. In addition, unlike observations of astrophysical sources at virtually infinite distances, near-target observations of planetary bodies introduce a unique set of challenges. While true focusing X-ray optics can overcome these challenges, a practical implementation of focusing X-ray optics for planetary missions depends on the feasibility of compact lightweight X-ray optics. We review scientific motivations for X-ray observations of planetary bodies and illustrate the unique challenges encountered in planetary missions through a few examples. We introduce a new metal-ceramic hybrid technology for X-ray mirrors that can enable compact lightweight Wolter-I X-ray optics suitable for resource limited planetary missions.
Development of light weight replicated x-ray optics, II
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NASA’S future X-ray astronomy missions will require X-ray optics that have large effective area while remaining lightweight, and cost effective. Some X-ray missions, such as XMM-Newton[1] , and the upcoming Spectrum-Röntgen- Gamma[2] mission use an electroformed nickel replication (ENR) process[3] to fabricate the nested grazing incidence X-ray telescope mirror shells for an array of moderate resolution, moderate effective area telescopes. We are developing a process to fabricate metal-ceramic replicated optics which will be lighter weight than current nickel replicated technology. Our technology development takes full advantage of the replication technique by fabricating large diameter mirrors with thin cross sections allowing maximum nesting and increase in collecting area. This will lead to future cost effective missions with large effective area and lightweight optics with good angular resolution. Recent results on fabrication and testing of these optics is presented.
Instrumentation for Polarimetry
A high-energy Compton polarimeter for the POET SMEX mission
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The primary science goal of the Polarimeters for Energetic Transients (POET) mission is to measure the polarization of gamma-ray bursts over a wide energy range, from X rays to soft gamma rays. The higher-energy portion of this band (50 - 500 keV) will be covered by the High Energy Polarimeter (HEP) instrument, a non-imaging, wide field of view Compton polarimeter. Incident high-energy photons will Compton scatter in low-Z, plastic scintillator detector elements and be subsequently absorbed in high-Z, CsI(Tl) scintillator elements; polarization is detected by measuring an asymmetry in the azimuthal scatter angle distribution. The HEP design is based on our considerable experience with the development and flight of the Gamma-Ray Polarimeter Experiment (GRAPE) balloon payload. We present the design of the POET HEP instrument, which incorporates lessons learned from the GRAPE balloon design and previous work on Explorer proposal efforts, and its expected performance on a two-year SMEX mission.
WPOL: a DSSD-based hard x-ray wide field imager and polarimeter
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WPOL (Wide field camera with POLarimetry) is a wide field camera which aims to monitor the X-ray/low gamma-ray sources and measures their polarimetric properties. This camera will be operated in space to trigger a main instrument in case of transient events (gamma-ray bursts, black hole binaries state transition, supernovae, …) and to map the Xray/ gamma-ray polarized sources of the Galaxy, which has never been done up to now. It will be proposed, as an accompanying instrument, in the context of the next medium mission ESA call (M4). The concept of the instrument is based upon a coded mask imaging with a detector unit composed of two planes of Silicon double sided stripped detectors (DSSD), a passive collimator and a tungsten mask. Mapping is done on the first plane through mask imaging and polarization is measured by studying Compton scattering events between the two planes. The source direction in the sky being known through the mask pattern projected on the detector plane, and the scattered photon direction being measured between the two planes, only the determination of the first energy deposit is needed to compute the whole Compton scattering kinetics and in particular, to determine the source photon energy
The use of laterally graded multilayer mirrors for soft X-ray polarimetry
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ABSTRACT We present continued development of laterally graded multilayer mirrors (LGMLs) for a telescope design capable of measuring linear X-ray polarization over a broad spectral band. The multilayer-coated mirrors are used as Bragg re ectors at the Brewster angle. By matching to the dispersion of a spectrometer, one may take advantage of high multilayer re ectivities and achieve modulation factors over 50% over the entire 0.2-0.8 keV band. In Phase II of the polarimetry beam-line development, we demonstrated that the system provides 100% polarized X-rays at 0.525 keV (Marshall et al. 2013). Here, we present results from phase III of our development, where a LGML is used at the source and laterally manipulated in order to select and polarize X-rays from emission lines for a variety of source anodes. The beam-line will then provide the capability to test polarimeter components across the 0.15-0.70 keV band. We also present plans for a suborbital rocket experiment designed to detect a polarization level of better than 10% for an active galactic nucleus.
Development of the depth-graded multilayers for XTP mission
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X-ray Timing and Polarization (XTP) mission will use focusing optics and advanced detector technology to be dedicated to the study of Black Hole, Neutron Star, Quark Star and the physics under extreme gravity, density and magnetism. XTP is expected to make the most sensitive temporal and polarization observations with good energy resolution in 1-30 keV with a detection area of ~1 square meter and a combination of various types of X-ray telescopes. We present a recent overview on the depth-graded multilayers coated on segmented glass optics used in XTP Telescope. This presentation will focus on improving the design, fabrication and characterization of grazing incident depth-graded multilayers based on the requirements of XTP. We discuss metrology on X-ray reflectivity and scatter of grazing incident depth-graded multilayers. We also present the future plan of making more depth-graded multilayers on thermally-slumped glass uesd in several prototype optics.
HARPO: a TPC as a gamma-ray telescope and polarimeter
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A gas Time Projection Chamber can be used for gamma-ray astronomy with excellent angular-precision and sensitivity to faint sources, and for polarimetry, through the measurement of photon conversion to e+e− pairs. We present the expected performance in simulations and the recent development of a demonstrator for tests in a polarized photon beam.
Design improvements and x-ray performance of a time projection chamber polarimeter for persistent astronomical sources
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The design of the Time-Projection Chamber (TPC) Polarimeter for the Gravity and Extreme Magnetism Small Explorer (GEMS) was demonstrated to Technology Readiness Level 6 (TRL-6)3 and the flight detectors fabricated, assembled and performance tested. A single flight detector was characterized at the Brookhaven National Laboratory Synchrotron Light Source with polarized X-rays at 10 energies from 2.3–8.0 keV at five detector positions. The detector met all of the GEMS performance requirements. Lifetime measurements have shown that the existing flight design has 23 years of lifetime4, opening up the possibility of relaxing material requirements, in particular the consideration of the use of epoxy, to reduce risk elsewhere. We report on design improvements to the GEMS detector to enable a narrower transfer gap that, when operated with a lower transfer field, reduces asymmetries in the detector response. In addition, the new design reduces cost and risk by simplifying the assembly and reducing production time. Finally, we report on the performance of the narrow-gap detector in response to polarized and unpolarized X-rays.
MAXI and NuStar
MAXI: all-sky observation from the International Space Station
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Monitor of All-sky X-ray Image (MAXI) is mounted on the International Space Station (ISS). Since 2009 it has been scanning the whole sky in every 92 minutes with ISS rotation. Due to high particle background at high latitude regions the carbon anodes of three GSC cameras were broken. We limit the GSC operation to low-latitude region around equator. GSC is suffering a double high background from Gamma-ray altimeter of Soyuz spacecraft. MAXI issued the 37-month catalog with 500 sources above ~0.6 mCrab in 4-10 keV. MAXI issued 133 to Astronomers Telegram and 44 to Gammaray burst Coordinated Network so far. One GSC camera had a small gas leak by a micrometeorite. Since 2013 June, the 1.4 atm Xe pressure went down to 0.6 atm in 2014 May 23. By gradually reducing the high voltage we keep using the proportional counter. SSC with X-ray CCD has detected diffuse soft X-rays in the all-sky, such as Cygnus super bubble and north polar spur, as well as it found a fast soft X-ray nova MAXI J0158-744. Although we operate CCD with charge-injection, the energy resolution is degrading. In the 4.5 years of operation MAXI discovered 6 of 12 new black holes. The long-term behaviors of these sources can be classified into two types of the outbursts, 3 Fast Rise Exponential Decay (FRED) and 3 Fast Rise and Flat Top (FRFT). The cause of types is still unknown.
The nuclear spectroscopic telescope array (NuSTAR) high-energy X-ray mission
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The Nuclear Spectroscopic Telescope Array (NuSTAR) mission was launched on 2012 June 13 and is the first focusing high-energy X-ray telescope in orbit operating above ~10 keV. NuSTAR flies two co-aligned Wolter-I conical approximation X-ray optics, coated with Pt/C and W/Si multilayers, and combined with a focal length of 10.14 meters this enables operation from 3-79 keV. The optics focus onto two focal plane arrays, each consisting of 4 CdZnTe pixel detectors, for a field of view of 12.5 arcminutes. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity, and with an effective point spread function FWHM of 18 arcseconds (HPD ~1), NuSTAR provides a leap of improvement in resolution over the collimated or coded mask instruments that have operated in this bandpass. We present in-orbit performance details of the observatory and highlight important science results from the first two years of the mission.
In-flight PSF calibration of the NuSTAR hard X-ray optics
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We present results of the point spread function (PSF) calibration of the hard X-ray optics of the Nuclear Spectroscopic Telescope Array (NuSTAR). Immediately post-launch, NuSTAR has observed bright point sources such as Cyg X-1, Vela X-1, and Her X-1 for the PSF calibration. We use the point source observations taken at several off-axis angles together with a ray-trace model to characterize the in-orbit angular response, and find that the ray-trace model alone does not fit the observed event distributions and applying empirical corrections to the ray-trace model improves the fit significantly. We describe the corrections applied to the ray-trace model and show that the uncertainties in the enclosed energy fraction (EEF) of the new PSF model is (approximately less than) 3% for extraction apertures of R (approximately greater than) 60″ with no significant energy dependence. We also show that the PSF of the NuSTAR optics has been stable over a period of ~300 days during its in-orbit operation.
Inflight performance and calibration of the NuSTAR CdZnTe pixel detectors
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The Nuclear Spectroscopic Telescope Array (NuSTAR) satellite is a NASA Small Explorer mission designed to operate the first focusing high-energy X-ray (3-79 keV) telescope in orbit. Since the launch in June 2012, all the NuSTAR components have been working normally. The focal plane module is equipped with an 155Eu radioactive source to irradiate the CdZnTe pixel detectors for independent calibration separately from optics. The inflight spectral calibration of the CdZnTe detectors is performed with the onboard 155Eu source. The derived detector performance agrees well with ground-measured data. The in-orbit detector background rate is stable and the lowest among past high-energy X-ray instruments.
Future Missions I: Astrosat and Spektrum-Roentgen Gamma
ASTROSAT mission
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ASTROSAT is India’s first astronomy satellite that will carry an array of instruments capable of simultaneous observations in a broad range of wavelengths: from the visible, near ultraviolet (NUV), far-UV (FUV), soft X-rays to hard X-rays. There will be five principal scientific payloads aboard the satellite: (i) a Soft X-ray Telescope (SXT), (ii) three Large Area Xenon Proportional Counters (LAXPCs), (iii) a Cadmium-Zinc-Telluride Imager (CZTI), (iv) two Ultra-Violet Imaging Telescopes (UVITs) one for visible and near-UV channels and another for far-UV, and (v) three Scanning Sky Monitors (SSMs). It will also carry a charged particle monitor (CPM). Almost all the instruments have qualified and their flight models are currently in different stages of integration into the satellite structure in ISRO Satellite Centre. ASTROSAT is due to be launched by India’s Polar Satellite Launch Vehicle (PSLV) in the first half of 2015 in a circular 600 km orbit with inclination of ~6 degrees, from Sriharikota launching station on the east coast of India. A brief description of the design, construction, capabilities and scientific objectives of all the main scientific payloads is presented here. A few examples of the simulated observations with ASTROSAT and plans to utilize the satellite nationally and internationally are also presented.
eROSITA on SRG
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eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is now officially scheduled for launch on March 26, 2016. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z < 1 in order to study the large scale structure in the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGN, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars and diffuse emission within the Galaxy. eROSITA is currently (June 2014) in its flight model and calibration phase. All seven flight mirror modules (+ 1 spare) have been delivered and measured in X-rays. The first camera including the complete electronics has been extensively tested (vacuum + X-rays). A pre-test of the final end-toend test has been performed already. So far, all subsystems and components are well within their expected performances.
Status of ART-XC/SRG instrument
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Spectrum Roentgen Gamma (SRG) is an X-ray astrophysical observatory, developed by Russia in collaboration with Germany. The mission will be launched in March 2016 from Baikonur, by a Zenit rocket with a Fregat booster and placed in a 6-month-period halo orbit around L2. The scientific payload consists of two independent telescopes – a softx- ray survey instrument, eROSITA, being provided by Germany and a medium-x-ray-energy survey instrument ART-XC being developed by Russia. ART-XC will consist of seven independent, but co-aligned, telescope modules. The NASA Marshall Space Flight Center (MSFC) is fabricating the flight mirror modules for the ART-XC/SRG. Each mirror module will be aligned with a focal plane CdTe double-sided strip detector which will operate over the energy range of 6−30 keV, with an angular resolution of <1′, a field of view of ~34′ and an expected energy resolution of about 10% at 14 keV.
ART-XC/SRG: status of the x-ray optics development
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The Astronomical Roentgen Telescope (ART) instrument is a hard-x-ray instrument with energy response up to 30 keV that is to be launched on board of the Spectrum Roentgen Gamma (SRG) Mission. The instrument consists of seven identical mirror modules coupled with seven CdTe strip focal-plane detectors. The mirror modules are being developed at the Marshall Space Flight Center (MSFC.) Each module has ~65 sq. cm effective area and an on-axis angular resolution of 30 arcseconds half power diameter (HPD) at 8 keV. The current status of the mirror module development and testing will be presented.
Report on the eROSITA camera system
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The eROSITA space telescope is currently developed for the determination of cosmological parameters and the equation of state of dark energy via evolution of clusters of galaxies. Furthermore, the instrument development was strongly motivated by the intention of a first imaging X-ray all-sky survey enabling measurements above 2 keV. eROSITA is a scientific payload on the Russian research satellite SRG. Its destination after launch is the Lagrangian point L2. The observational program of the observatory divides into an all-sky survey and pointed observations and takes in total about 7.5 years. The instrument comprises an array of 7 identical and parallel aligned telescopes. Each of the seven focal plane cameras is equipped with a PNCCD detector, an enhanced type of the XMM-Newton focal plane detector. This instrumentation permits spectroscopy and imaging of X-rays in the energy band from 0.3 keV to 10 keV with a field of view of 1.0 degree. The camera development is done at the Max-Planck-Institute for extraterrestrial physics. Key component of each camera is the PNCCD chip. This silicon sensor is a back-illuminated, fully depleted and column-parallel type of charge coupled device. The image area of the 450 micron thick frame-transfer CCD comprises an array of 384 x 384 pixels, each with a size of 75 micron x 75 micron. Readout of the signal charge that is generated by an incident X-ray photon in the CCD is accomplished by an ASIC, the so-called eROSITA CAMEX. It provides 128 parallel analog signal processing channels but multiplexes the signals finally to one output which feeds the detector signals to a fast 14-bit ADC. The read noise of this system is equivalent to a noise charge of about 2.5 electrons rms. We achieve an energy resolution close to the theoretical limit given by Fano noise (except for very low energies). For example, the FWHM at an energy of 5.9 keV is approximately 140 eV. The complete camera assembly comprises the camera head with the detector as key component, the electronics for detector operation as well as data acquisition and the filter wheel unit. In addition to the on-chip light blocking filter directly deposited on the photon entrance window of the PNCCD, an external filter can be moved in front of the sensor, which serves also for contamination protection. Furthermore, an on-board calibration source emitting several fluorescence lines is accommodated on the filter wheel mechanism for the purpose of in-orbit calibration. Since the spectroscopic silicon sensors need cooling down to -95°C to mitigate best radiation damage effects, an elaborate cooling system is necessary. It consists of two different types of heat pipes linking the seven detectors to two radiators. Based on the tests with an engineering model, a flight design was developed for the camera and a qualification model has been built. The tests and the performance of this camera is presented in the following. In conclusion an outlook on the flight cameras is given.
The calibration and testing of the eROSITA X-ray mirror assemblies
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In 2016 the X-ray Survey Telescope eROSITA, designed and built at MPE, will be launched on the Russian Spektr- Roentgen-Gamma Mission. A compact bundle of 7 co-aligned mirror modules with a focal length of 1600 mm and 54 nested mirror shells each form the X-ray telescope. The sensitivity of the telescope in terms of effective area, field-ofview (61'), and angular resolution (~16" HEW on-axis) will yield a high grasp of about 1000 cm2 deg2 around 1 keV with an average angular resolution of ~26" HEW over the field-of-view (30" including optical and spacecraft error contributions). All flight mirror modules including a flight spare have been completed and passed their acceptance tests in December 2013. The mirror modules now have all been mated with their corresponding X-ray baffles to form mirror assemblies and the passed rigorous environmental vibration and thermal cycling tests. Here we report on the results of these measurements and on the calibration measurements planned for the completed flight mirror assemblies.
Future Missions II: Neutron Stars to Gamma-ray Bursts
Estimation of observation possibility of the x-ray interferometer with an x-ray beam-splitter
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We report our recent activities for a development of a new X-ray interferometer with a beam splitter and discuss a possible observation of some celestial objects. The X-ray interferometer consists of two flat mirrors and one flat beam splitter. Samples of the beam splitter and the mirrors have been designed and fabricated. We measured the reflectivity of the mirrors and the reflectivity and transmission of the beam splitters with a synchrotron source at KEK-PF. Obtained results of the mirrors are roughly consistent with the design values, but the reflectivity of the beam splitter is roughly half of the design value. Using these measured values, we estimated required area and observation-time to obtain fringe signals of celestial objects. We concluded that a broad-band interferometer using non-dispersive high spectral resolution detector, such as the micro-calorimeter array, is essential for the future development.
The neutron star interior composition explorer (NICER): mission definition
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Over a 10-month period during 2013 and early 2014, development of the Neutron star Interior Composition Explorer (NICER) mission [1] proceeded through Phase B, Mission Definition. An external attached payload on the International Space Station (ISS), NICER is scheduled to launch in 2016 for an 18-month baseline mission. Its prime scientific focus is an in-depth investigation of neutron stars—objects that compress up to two Solar masses into a volume the size of a city—accomplished through observations in 0.2–12 keV X-rays, the electromagnetic band into which the stars radiate significant fractions of their thermal, magnetic, and rotational energy stores. Additionally, NICER enables the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration of spacecraft navigation using pulsars as beacons. During Phase B, substantive refinements were made to the mission-level requirements, concept of operations, and payload and instrument design. Fabrication and testing of engineering-model components improved the fidelity of the anticipated scientific performance of NICER’s X-ray Timing Instrument (XTI), as well as of the payload’s pointing system, which enables tracking of science targets from the ISS platform. We briefly summarize advances in the mission’s formulation that, together with strong programmatic performance in project management, culminated in NICER’s confirmation by NASA into Phase C, Design and Development, in March 2014.
Introduction to the hard x-ray modulation telescope
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The Hard X-ray Modulation Telescope (HXMT) is China’s first astronomical satellite. Based on the Direct Demodulation Method (DDM), it was designed to reconstructs images from data obtained in a scanning mode. Although this project was delayed by about 15 years, it will still bring us merits in some key sciences of observing the galactic transients and measuring the diffuse X-ray emission. This satellite is currently in the phase of flight model production with the expected launch in late 2015.
The French payload on-board the SVOM French-Chinese mission
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The SVOM (Space-based multi-band astronomical Variable Objects Monitor) French-Chinese mission is dedicated to the detection, localization and study of Gamma Ray Bursts (GRBs) and other high-energy transient phenomena. We first present the major principles of the SVOM system including the alert system providing near-real-time GRB localizations to large ground-based telescopes. Then the paper describes the definition of the SVOM payload and more particularly the French payload composed of the ECLAIRs instrument, dedicated to GRB detection and positioning, and the MXT instrument, dedicated to GRB followup observation in soft X-ray band.
The microchannel x-ray telescope for the gamma-ray burst mission SVOM
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We present the Microchannel X-ray Telescope, a new light and compact focussing telescope that will be ying on the Sino-French SVOM mission dedicated to Gamma-Ray Burst science. The MXT design is based on the coupling of square pore micro-channel plates with a low noise pnCCD. MXT will provide an effective area of about 50 cm2, and its point spread function is expected to be better than 3.7 arc min (FWHM) on axis. The estimated sensitivity is adequate to detect all the afterglows of the SVOM GRBs, and to localize them to better then 60 arc sec after five minutes of observation.
The x-/gamma-ray camera ECLAIRs for the gamma-ray burst mission SVOM
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We present ECLAIRs, the Gamma-ray burst (GRB) trigger camera to fly on-board the Chinese-French mission SVOM. ECLAIRs is a wide-field (~ 2 sr) coded mask camera with a mask transparency of 40% and a 1024 cm2 detection plane coupled to a data processing unit, so-called UGTS, which is in charge of locating GRBs in near real time thanks to image and rate triggers. We present the instrument science requirements and how the design of ECLAIRs has been optimized to increase its sensitivity to high-redshift GRBs and low-luminosity GRBs in the local Universe, by having a low-energy threshold of 4 keV. The total spectral coverage ranges from 4 to 150 keV. ECLAIRs is expected to detect ~ 200 GRBs of all types during the nominal 3 year mission lifetime.
To reach a 4 keV low-energy threshold, the ECLAIRs detection plane is paved with 6400 4 × 4 mm2 and 1
mm-thick Schottky CdTe detectors. The detectors are grouped by 32, in 8×4 matrices read by a low-noise ASIC, forming elementary modules called XRDPIX. In this paper, we also present our current efforts to investigate the performance of these modules with their front-end electronics when illuminated by charged particles and/or photons using radioactive sources. All measurements are made in different instrument configurations in vacuum and with a nominal in-flight detector temperature of −20°C. This work will enable us to choose the in-flight configuration that will make the best compromise between the science performance and the in-flight operability of ECLAIRs. We will show some highlights of this work.
Future Missions III: ASTRO-H
The ASTRO-H X-ray astronomy satellite
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The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of ΔE ≤ 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.
ASTRO-H Hard X-ray Telescope (HXT)
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The new Japanese X-ray Astronomy satellite, ASTRO-H will carry two identical hard X-ray telescopes (HXTs), which cover 5 to 80 keV, in order to provide new insights into frontier of X-ray astronomy. The HXT mirror surfaces are coated with Pt/C depth-graded multilayers to enhance hard X-ray effective area by means of Bragg reflection, and 213 mirror reflectors with a thickness of 0.22 mm are tightly nested confocally in a telescope. The production of FM HXT-1 and HXT-2 were completed in 2012 and 2013, respectively. The X-ray performance of HXTs were measured at the synchrotron radiation facility SPring-8/ BL20B2 Japan. The total effective area of two HXTs is about 350 cm2 at 30 keV and the angular resolution of HXT is about 1.’9 in half power diameter at 30 keV. The HXTs are in the clean room at ISAS for waiting the final integration test.
The Hard X-ray Imager (HXI) for the ASTRO-H Mission
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The 6th Japanese X-ray satellite, ASTRO-H, is scheduled for launch in 2015. The hard X-ray focusing imaging system will observe astronomical objects with the sensitivity for detecting point sources with a brightness of 1/100,000 times fainter than the Crab nebula at > 10 keV. The Hard X-ray Imager (HXI) is a focal plane detector 12 m below the hard X-ray telescope (HXT) covering the energy range from 5 to 80 keV. The HXI is composed of a stacked Si/CdTe semiconductor detector module and surrounding BGO scintillators. The latter work as active shields for efficient reduction of background events caused by cosmic-ray particles, cosmic X-ray background, and in-orbit radiation activation. In this paper, we describe the detector system, and present current status of flight model development, and performance of HXI using an engineering model of HXI.
ASTRO-H Soft X-ray Telescope (SXT)
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ASTRO-H is an astrophysics satellite dedicated for non-dispersive X-ray spectroscopic study on selective celestial X-ray sources. Among the onboard instruments there are four Wolter-I X-ray mirrors of their reflectors’ figure in conical approximation. Two of the four are soft X-ray mirrors1, of which the energy range is from a few hundred eV to 15 keV within the effective aperture being defined by the nested reflectors’ radius ranging between 5.8 cm to 22.5 cm. The focal point instruments will be a calorimeter (SXS) and a CCD camera (SXI), respectively. The mirrors were in quadrant configuration with photons being reflected consecutively in the primary and secondary stage before converging on the focal plane of 5.6 m away from the interface between the two stages. The reflectors of the mirror are made of heat-formed aluminum substrate of the thickness gauged of 152 μm, 229 μm, and 305 μm of the alloy 5052 H-19, followed by epoxy replication on gold-sputtered smooth Pyrex cylindrical mandrels to acquire the X-ray reflective surface. The epoxy layer is 10 m nominal and surface gold layer of 0.2 μm. Improvements on angular response over its predecessors, e.g. Astro-E1/Suzaku mirrors, come from error reduction on the figure, the roundness, and the grazing angle/radius mismatching of the reflecting surface, and tighter specs and mechanical strength on supporting structure to reduce the reflector positioning and the assembly errors. Each soft x-ray telescope (SXT), SXT-1 or SXT-2, were integrated from four independent quadrants of mirrors. The stray-light baffles, in quadrant configuration, were mounted onto the integrated mirror. Thermal control units were attached to the perimeter of the integrated mirror to keep the mirror within operating temperature in space. The completed instrument went through a series of optical alignment, thus made the quadrant images confocal and their optical axes in parallel to achieve highest throughput possible. Environmental tests were carried out, and optical quality of the telescopes has been confirmed. SXT-1 and -2 were tested with the broad but slightly divergent beam, up to 8 arc-minutes, at Goddard. The full characterization were carried out in Japan which includes: angular resolution, effective area in the energy range of ~ 0.4 – 12keV, off-axis response at various energies, etc. We report the calibration results of the SXT-1 and -2 that were obtained at NASA/Goddard and JAXA/ISAS. The detailed calibration are reported in the two papers in this conference: 9144-206, "Ground-based x-ray calibration of the ASTRO-H soft x-ray telescopes" by R. Iizuka et al. and 9144-207, "Revealing a detailed performance of the soft x-ray telescopes of the ASTRO-H mission" by T. Sato, et al. Some small but significant discrepancies existed between ISAS and Goddard measurements that were attributed to the difference of the X-ray beams - pencil beam vs divergent beam.
Soft X-ray Imager (SXI) onboard ASTRO-H
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Soft X-ray Imager (SXI) is a CCD camera onboard the ASTRO-H satellite which is scheduled to be launched in 2015. The SXI camera contains four CCD chips, each with an imaging area of 31mm x 31 mm, arrayed in mosaic, covering the whole FOV area of 38′ x 38′. The CCDs are a P-channel back-illuminated (BI) type with a depletion layer thickness of 200 _m. High QE of 77% at 10 keV expected for this device is an advantage to cover an overlapping energy band with the Hard X-ray Imager (HXI) onboard ASTRO-H. Most of the flight components of the SXI system are completed until the end of 2013 and assembled, and an end-to-end test is performed. Basic performance is verified to meet the requirements. Similar performance is confirmed in the first integration test of the satellite performed in March to June 2014, in which the energy resolution at 5.9 keV of 160 eV is obtained. In parallel to these activities, calibrations using engineering model CCDs are performed, including QE, transmission of a filter, linearity, and response profiles.
Soft x-ray spectrometer (SXS): the high-resolution cryogenic spectrometer onboard ASTRO-H
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We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.
Soft gamma-ray detector (SGD) onboard the ASTRO-H mission
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The Soft Gamma-ray Detector (SGD) is one of observational instruments onboard the ASTRO-H, and will provide 10 times better sensitivity in 60{600 keV than the past and current observatories. The SGD utilizes similar technologies to the Hard X-ray Imager (HXI) onboard the ASTRO-H. The SGD achieves low background by constraining gamma-ray events within a narrow field-of-view by Compton kinematics, in addition to the BGO active shield. In this paper, we will present the results of various tests using engineering models and also report the flight model production and evaluations.
The Next Generation: Athena I
Science requirements and optimization of the silicon pore optics design for the Athena mirror
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The science requirements for the Athena X-ray mirror are to provide a collecting area of 2 m2 at 1 keV, an angular resolution of ~5 arc seconds half energy eidth (HEW) and a field of view of diameter 40-50 arc minutes. This combination of area and angular resolution over a wide field are possible because of unique features of the Silicon pore optics (SPO) technology used. Here we describe the optimization and modifications of the SPO technology required to achieve the Athena mirror specification and demonstrate how the optical design of the mirror system impacts on the scientific performance of Athena.
Preparing the optics technology to observe the hot universe
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With the selection of “The hot and energetic Universe” as science theme for ESA's second large class mission (L2) in the Cosmic Vision programme, work is focusing on the technology preparation for an advanced X-ray observatory. The core enabling technology for the high performance mirror is the Silicon Pore Optics (SPO) [1 to 23], a modular X-ray optics technology, which utilises processes and equipment developed for the semiconductor industry. The paper provides an overview of the programmatic background, the status of SPO technology and gives an outline of the development roadmap and activities undertaken and planned by ESA on optics, coatings [24 to 30] and test facilities [31, 33].
Making the ATHENA optics using silicon pore optics
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Silicon Pore Optics, after 10 years of development, forms now the basis for future large (L) class astrophysics Xray observatories, such as the ATHENA mission to study the hot and energetic universe, matching the L2 science theme recently selected by ESA for launch in 2028. The scientific requirements result in an optical design that demands high angular resolution (5“) and large effective area (2 m2 at a few keV) of an X-ray lens with a focal length of 12 to14 m. Silicon Pore Optics was initially based on long (25 to 50 m) focal length telescope designs, which could achieve several arc second angular resolution by curving the silicon mirror in only one direction (conical approximation). With the advent of shorter focal length missions we started to develop mirrors having a secondary curvature, allowing the production of Wolter-I type optics, which are on axis aberration-free. In this paper we will present the new manufacturing process, discuss the impact of the ATHENA optics design on the technology development and present the results of the latest X-ray test campaigns.
Qualification of silicon pore optics
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Silicon Pore Optics (SPO) are the enabling technology for ESA’s second large class mission in the Cosmic Vision programme. As for every space hardware, a critical qualification process is required to verify the suitability of the SPO mirror modules surviving the launch loads and maintaining their performance in the space environment. We present recent design modifications to further strengthen the mounting system (brackets and dowel pins) against mechanical loads. The progress of a formal qualification test campaign with the new mirror module design is shown. We discuss mechanical and thermal limitations of the SPO technology and provide recommendations for the mission design of the next X-ray Space Observatory.
The Next Generation: Athena II
The wide field imager instrument for Athena
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The "Hot and Energetic Universe" has been selected as the science theme for ESA's L2 mission, scheduled for launch in 2028. The proposed Athena X-ray observatory provides the necessary capabilities to achieve the ambitious goals of the science theme. The X-ray mirrors are based on silicon pore optics technology and will have a 12 m focal length. Two complementary camera systems are foreseen which can be moved in and out of the focal plane by an interchange mechanism. These instruments are the actively shielded micro-calorimeter spectrometer X-IFU and the Wide Field Imager (WFI). The WFI will combine an unprecedented survey power through its large field of view of 40 arcmin with a high countrate capability (approx. 1 Crab). It permits a state-of-the-art energy resolution in the energy band of 0.1 keV to 15 keV during the entire mission lifetime (e.g. FWHM ≤ 150 eV at 6 keV). This performance is accomplished by a set of DEPFET active pixel sensor matrices with a pixel size matching the angular resolution of 5 arcsec (on-axis) of the mirror system. Each DEPFET pixel is a combined detector-amplifier structure with a MOSFET integrated onto a fully depleted 450 micron thick silicon bulk. The signal electrons generated by an X-ray photon are collected in a so-called internal gate below the transistor channel. The resulting change of the conductivity of the transistor channel is proportional to the number of electrons and thus a measure for the photon energy. DEPFETs have already been developed for the "Mercury Imaging X-ray Spectrometer" on-board of ESA’s BepiColombo mission. For Athena we develop enhanced sensors with integrated electronic shutter and an additional analog storage area in each pixel. These features improve the peak-to-background ratio of the spectra and minimize dead time. The sensor will be read out with a new, fast, low-noise multi-channel analog signal processor with integrated sequencer and serial analog output. The architecture of sensor and readout ASIC allows readout in full frame mode and window mode as well by addressing selectively arbitrary sub-areas of the sensor allowing time resolution in the order of 10 μs. The further detector electronics has mainly the following tasks: digitization, pre-processing and telemetry of event data as well as supply and control of the detector system. Although the sensor will already be equipped with an on-chip light blocking filter, a filter wheel is necessary to provide an additional external filter, an on-board calibration source, an open position for outgassing, and a closed position for protection of the sensor. The sensor concept provides high quantum efficiency over the entire energy band and we intend to keep the instrumental background as low as possible by designing a graded Z-shield around the sensor. All these properties make the WFI a very powerful survey instrument, significantly surpassing currently existing observatories and in addition allow high-time resolution of the brightest X-ray sources with low pile-up and high efficiency. This manuscript will summarize the current instrument concept and design, the status of the technology development, and the envisaged baseline performance.
Prospects and limitations of DEPFET active pixel sensors as high speed spectroscopic x-ray imager for the ATHENA wide field imager
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Since many years DEPFETs have been developed for space and ground based X-ray imaging and spectroscopy experiments. Prototypes have been successfully tested and qualified. Over the past years, the DEPFET technology was improved and additional features of DEPFETs were developed: increase of dynamic range, improvement of radiation hardness, implementation of electronic shutters, integration of an analog storage, reduction of readout noise and improvement of the low energy performance. This paper will present two novel DEPFET concepts which are able to fulfill the demanding requirements of the proposed ATHENA Wide Field Imager. It will summarize the most important DEPFET characteristics on the basis of measurements and device simulations, taking into account the given boundary conditions of the mission.
The X-ray Integral Field Unit (X-IFU) for Athena
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Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), offering 2:5 eV spectral resolution, with ~5" pixels, over a field of view of 50 in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain.
Development of TES-based detectors array for the X-ray Integral Field Unit (X-IFU) on the future x-ray observatory ATHENA
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We are developing transition-edge sensor (TES)-based microcalorimeters for the X-ray Integral Field Unit (XIFU) of the future European X-Ray Observatory Athena. The microcalorimeters are based on TiAu TESs coupled to 250μm squared, AuBi absorbers. We designed and fabricated devices with different contact geometries between the absorber and the TES to optimise the detector performance and with different wiring topology to mitigate the self-magnetic field. The design is tailored to optimise the performance under Frequency Domain Multiplexing. In this paper we review the main design feature of the pixels array and we report on the performance of the 18 channels, 2-5MHz frequency domain multiplexer that will be used to characterised the detector array.
Background simulations for the ATHENA X-IFU instrument: impact on the instrumental design
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On 28 november 2013 ESA selected “The Hot and Energetic Universe” as the scientific theme for a large mission to be flown in 2028 in the second lagrangian point, and ATHENA is the mission that will address this science topic. It will carry on board the X-ray Integral Field Unit (X-IFU), a 3840 pixel array based on TES (Transition Edge Sensor) microcalorimeters providing high resolution spectroscopy (2.5 eV @ 6 keV) in the 0.3-12 keV range. Among X-IFU goals there is the detection and characterization of high redshift AGNs, Clusters of galaxies and their outskirts, and the elusive Warm Hot Intergalactic Medium (WHIM), so great care must be paid to the reduction of the background level. These scientific objectives will be reached if the particle background is kept lower than 0.05 cts cm−2 s−1, and to this aim, it is mandatory the use of a Cryogenic AC (CryoAC), as well as an optimized design of the cryostat and of the structures surrounding X-IFU. Our team, that is responsible for the ACD design, performed a detailed study to predict the rejection efficiency of the ACD as a function of its geometrical parameters and design choices. Since no experimental data on the background experienced by X-Ray microcalorimeters in the L2 orbit are available at the moment, the particle background levels have been calculated by means of Monte Carlo simulations using the Geant4 software.
The Next Generation: Small Mission Concepts
Wide-field MAXI: soft x-ray transient monitor on the ISS
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WF-MAXI is a soft X-ray transient monitor proposed for the ISS/JEM. Unlike MAXI, it will always cover a large field of view (20 % of the entire sky) to detect short transients more efficiently. In addition to the various transient sources seen by MAXI, we hope to localize X-ray counterparts of gravitational wave events, expected to be directly detected by Advanced-LIGO, Virgo and KAGRA in late 2010's. The main instrument, the Soft X-ray Large Solid Angle Cameras (SLC) is sensitive in the 0.7-12 keV band with a localization accuracy of ~ 0:1°. The Hard X-ray Monitor (HXM) covers the same sky field in the 20 keV-1 MeV band.
DIOS: the dark baryon exploring mission
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DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2020 with JAXA’s Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a very wide field of view (30–50 arcmin diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth’s magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. We also consider revising the payload design to optimize the scientific capability allowed by the boundary conditions of the small mission.
Formation Flight Astronomical Survey Telescope (FFAST) mission in hard x-ray
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A formation flight astronomical survey telescope (FFAST) is a new project that will cover a large sky area in hard X-ray. In particular, it will focus on the energy range up to 80keV. It consists of two small satellites that will go in a formation flight. One is an X-ray telescope satellite carrying a super mirror, and the other is a detector satellite carrying an SDCCD. Two satellites are put into a low earth orbit in keeping the separation of 12m. This will survey a large sky area at hard X-ray region to study the evolution of the universe.
High-z gamma-ray bursts for unraveling the dark ages mission HiZ-GUNDAM
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We are now investigating and studying a small satellite mission HiZ-GUNDAM for future observation of gamma-ray bursts (GRBs). The mission concept is to probe “the end of dark ages and the dawn of formation of astronomical objects”, i.e. the physical condition of early universe beyond the redshift z > 7. We will consider two kinds of mission payloads, (1) wide field X-ray imaging detectors for GRB discovery, and (2) a near infrared telescope with 30 cm in diameter to select the high-z GRB candidates effectively. In this paper, we explain some requirements to promote the GRB cosmology based on the past observations, and also introduce the mission concept of HiZ-GUNDAM and basic development of X-ray imaging detectors.
The Next Generation: LOFT
The Large Observatory for x-ray timing
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The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m2 effective area, 2-30 keV, 240 eV spectral resolution, 1° collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.
The design of the wide field monitor for the LOFT mission
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LOFT (Large Observatory For x-ray Timing) is one of the ESA M3 missions selected within the Cosmic Vision program in 2011 to carry out an assessment phase study and compete for a launch opportunity in 2022-2024. The phase-A studies of all M3 missions were completed at the end of 2013. LOFT is designed to carry on-board two instruments with sensitivity in the 2-50 keV range: a 10 m2 class Large Area Detector (LAD) with a <1° collimated FoV and a wide field monitor (WFM) making use of coded masks and providing an instantaneous coverage of more than 1/3 of the sky. The prime goal of the WFM will be to detect transient sources to be observed by the LAD. However, thanks to its unique combination of a wide field of view (FoV) and energy resolution (better than 500 eV), the WFM will be also an excellent monitoring instrument to study the long term variability of many classes of X-ray sources. The WFM consists of 10 independent and identical coded mask cameras arranged in 5 pairs to provide the desired sky coverage. We provide here an overview of the instrument design, configuration, and capabilities of the LOFT WFM. The compact and modular design of the WFM could easily make the instrument concept adaptable for other missions.
The large area detector of LOFT: the Large Observatory for X-ray Timing
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LOFT (Large Observatory for X-ray Timing) is one of the five candidates that were considered by ESA as an M3 mission (with launch in 2022-2024) and has been studied during an extensive assessment phase. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. Its pointed instrument is the Large Area Detector (LAD), a 10 m2-class instrument operating in the 2-30keV range, which holds the capability to revolutionise studies of variability from X-ray sources on the millisecond time scales.
The LAD instrument has now completed the assessment phase but was not down-selected for launch. However, during the assessment, most of the trade-offs have been closed leading to a robust and well documented design that will be reproposed in future ESA calls. In this talk, we will summarize the characteristics of the LAD design and give an overview of the expectations for the instrument capabilities.
Poster Session
High efficiency CCD detectors at UV wavelengths
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The Faint Intergalactic Redshifted Emission Balloon (FIREBall) is a NASA/CNES balloon-borne ultraviolet multi-object spectrograph designed to observe the diffuse gas around galaxies (the circumgalactic medium) via line emission redshifted to ~205 nm. FIREBall uses a ultraviolet-optimized delta doped e2v CCD201 with a custom designed high efficiency five layer anti-reflection coating. This combination achieves very high quantum efficiency (QE) and photon-counting capability, a first for a CCD detector in this wavelength range. We also present new work on red blocking mirror coatings to reduce red leak.
Performance and validation of a suborbital FUV spatial heterodyne spectro-polarimeter optimized for wide-field observations of interplanetary hydrogen
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The HYdrogen Polarimetric Explorer (HYPE) is a sounding rocket experiment designed to obtained spectro-polarimetric measurements of diffuse ultraviolet astrophysical objects at high resolving power. HYPE consists of a spatial heterodyne spectrometer and a diamond Brewster - LiF half wave polarimeter and is optimized for study of solar scattering from interplanetary hydrogen penetrating the solar system. We report on the calibration and performance of HYPE in preparation for a first flight of the experiment.
Multi object spectrograph of the Fireball balloon experiment
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Fireball is a NASA/CNES balloon-borne experiment to study the faint diffuse circumgalactic emission in the ultraviolet around 200 nm. The field of view of the 1 meter diameter parabola is enlarged using a two-mirror field corrector providing 1000 arcmin2 at the slit mask. The 0.1 nm resolution Multi Object Spectrograph is based on two identical Schmidt systems sharing a reflective aspherical grating. The aspherization of the grating is achieved using a double replication technique of a metallic deformable matrix. We will present the F/2.5 spectrograph design and the deformable matrix process to obtain the Schmidt grating with elliptical contours.
SUAVE: a UV telescope for space weather and solar variability studies
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SUAVE (Solar Ultraviolet Advanced Variability Experiment) is a far ultraviolet (FUV) imaging solar telescope of novel design for ultimate thermal stability and long lasting performances. SUAVE is a 90 mm Ritchey- Chrétien telescope with SiC (Silicon Carbide) mirrors and no entrance window for long and uncompromised observations in the UV (no coatings of mirrors, flux limited to less than a solar constant on filters to avoid degradation), associated with an ultimate thermal control (heat evacuation, focus control, stabilization). Design of the telescope and early thermal modeling leading to a representative breadboard (a R and T program supported by CNES) will be presented. SUAVE is the main instrument of the SUITS (Solar Ultraviolet Influence on Troposphere/Stratosphere) microsatellite mission, a small-size mission proposed to CNES and ESA.
The FIREBall-2 UV sample grating efficiency at 200-208nm
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The FIREBall-2 (Faint Intergalactic Redshifted Emission Balloon-2) is a balloon-borne ultraviolet spectro-imaging mission optimized for the study of faint diffuse emission around galaxies. A key optical component of the new spectrograph design is the high throughput cost-effective holographic 2400 ℓ =mm, 110x130mm aspherized reflective grating used in the range 200 - 208nm, near 28°deviation angle. In order to anticipate the efficiency in flight conditions, we have developed a PCGrate model for the FIREBall grating calibrated on linearly polarized measurements at 12° deviation angle in the range 240-350nm of a 50x50mm replica of the same master selected for the flight grating. This model predicts an efficiency within [64:7; 64:9]±0:7% (S polarization) and [38:3; 45]±2:2% (P-polarization) for the baseline aluminum coated grating with an Al2O3 natural oxidation layer and within [63:5; 65] ±1% (S-polarization) and [51:3; 54:8] ±2:8% (P-polarization) for an aluminum plus a 70nm MgF2 coating, in the range 200 - 208nm and for a 28°deviation angle. The model also shows there is room for significant improvements at shorter wavelengths, of interest for future deep UV spectroscopic missions.
Improved ground calibration results from Southwest Research Institute Ultraviolet Radiometric Calibration Facility (UV-RCF)
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Four compact planetary ultraviolet spectrographs have been built by Southwest Research Institute and successfully operated on different planetary missions. These spectrographs underwent a series of ground radiometric calibrations before delivery to their respective spacecraft. In three of the four cases, the in-flight measured sensitivity was approximately 50% lower than the ground measurement. Recent tests in the Southwest Research Institute Ultraviolet Radiometric Calibration Facility (UV-RCF) explain the discrepancy between ground and flight results. Revised ground calibration results are presented for the Rosetta-Alice, New Horizons-Alice, the Lunar Reconnaissance Orbiter Lyman- Alpha Mapping Project, and Juno-Ultraviolet Spectrograph (UVS) and are then compared to the original ground and flight calibrations. The improved understanding of the calibration system reported here will result in improved ground calibration of the upcoming Jupiter Icy Moons Explorer (JUICE)-UVS.
An introduction to the IAAT ultraviolet MCP detector development
S. Hermanutz,
J. Barnstedt,
S. Diebold,
et al.
Show abstract
Observations of ultraviolet light is the key to understand high temperature processes in the universe like hot plasma, accretion processes or illuminated protoplanetary discs around UV sources. Furthermore these observation contribute to major cosmological questions, like the distribution of baryonic matter or the formation of the milky way, as pointed out by Gomez de Castro et al.1 Driven by the idea to participate in the Russian World Space Observatory we started to develop a position sensitive micro channel plate detector (MCP) for spectroscopy in the range of 160nm to 300 nm. Although we are not part of this project we still build a MCP detector prototype. In this paper we will present the general design of the detector and mainly focus on the aspect of our photocathode, while the electronics will be explained in more detail in the paper Characterisation of low power readout electronics for a UV microchannel plate detector with cross-strip readout" (Paper number 9144-116) by Marc Pfeifer.
New facilities for Al+MgF2 coating for 2-m class mirrors for UV
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The World Space Observatory--Ultraviolet (WSO--UV) project is a Russian-Spanish space mission for spectroscopic and imaging observations in the UV domain (115-320 nm) where some of the most important astrophysical processes can be efficiently studied with unprecedented capability. In the horizon of the next decade, WSO--UV will be the only mission with the large primary mirror fully devoted for UV studies. The observatory includes a 170 cm aperture telescope capable of high-resolution spectroscopy, long slit low-resolution spectroscopy, and deep UV imaging. The telescope T-170M is a Ritchey-Chrétien with a F/10 focal ratio and a corrected field of view of 0.5 degrees. Specific data on the WSO-UV project (telescope, satellite, orbit, launcher, ground segment, etc.) are given in [1-6]. The current status of the WSO-UV focal plane instruments, their status of implementation, and the expected performances are presented in [7]. The science drivers of the WSO-UV mission are described in [8, 9]. The main WSO-UV instruments, spectrographs (WUVS instrument) and imagers (ISSIS instrument) are described in [10-13] and [14-15] correspondingly. The prospects of stellar studies with WSO-UV are presented in papers [16-17]. A paper [18] describes our experience of using the DP-190 glue for adhesive attachment of a large space mirror and its rim. In the instrument compartment, see Figure 1, the optical bench (OB) – used as reference plane for all the onboard instrumentation – is aligned and maintained in the correct position with respect to the primary mirror (PM) using a three rods system. An imaging instrument ISSIS is mounted on the upper basis of the optical bench, in the space available between the PM and the OB itself, while spectrographs (WUVS instrument) are mounted to the OB bottom basis. One of the primary tasks in creating telescope’s PM is to apply coating with required reflective and protective properties. Aluminum is a well known reflecting coating for wavelength above 120 nm [19] with reflectivity more than 90% at wavelength longer than 200 nm, but the spectral range from 700 to 900 nm, where it’s lowest value of reflectivity is 86% at 850 nm. That makes aluminum one of the best coating materials in the creating a mirror for operations in vacuum ultraviolet. However, the aluminum membrane is prone to oxidization, so applying the protecting coating is essential. Magnesium fluoride is one of the few materials transparent in the UV range [20]. In this contribution, capacities of new facilities in LUCH company that are created for World Space Observatory – Ultraviolet (WSO-UV) project are described in Section 2, the process of applying Al + MgF2 coating workout is presented in Section 3, results of applying Al+MgF2 coating for WSO-UV primary mirror are presented in Section 4 and a brief summary are provided in the concluding Section 5.
Narrowband filters for the FUV range
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Space observations in the far ultraviolet (FUV, 100-200 nm) are aimed at providing essential information for astrophysics, solar physics, and atmosphere physics. There are key spectral lines and bands in the FUV for the above disciplines. Despite various developments in the recent decades, yet many observations are not possible due to technical limitations, of which one of the most important is the lack of efficient optical coatings. Hence for solar physics applications there are needs of narrowband coatings for key wavelengths such as H Lyman β (102.6 nm) and OVI lines (103.2 and 103.8 nm). For atmosphere physics, narrowband coatings are required for observations at spectral lines such as OI (135.6 nm) and at the N2 Lyman-Birge-Hopfield band (LBH, 127-240 nm). In solar corona observations, often the intensities of the target lines are weak, and this radiation may be masked by more intense lines, such as H Lyman α at 121.6 nm. Until now, no narrowband multilayers peaked in the ~100-105 nm range have been reported, which is due to the absorption of materials at these wavelengths. When efficient narrowband coatings are not possible, an option is the use of coatings with high reflectance at the target wavelength and simultaneously low reflectance at the undesired wavelength, such as Lyman α. We have developed novel multilayers to address this target, with combinations of these materials: Al, LiF, SiC and C. We developed multilayers based on the following three systems, Al/LiF/SiC, Al/LiF/SiC/C, and Al/LiF/SiC/LiF. Their reflectance was measured both when fresh and after some storage in a desiccator. Al/LiF/SiC and Al/LiF/SiC/C systems displayed a high Lyman β/Lyman α reflectance ratio when fresh, although they resulted in an undesired reflectance increase at Lyman α for the aged samples and the reflectance ratio Lyman β/Lyman α became small; this behavior turned these systems useless for the present application. The most promising multilayers were the ones based on the Al/LiF/SiC/LiF system, which resulted in a good performance and a limited evolution after months of storage in a desiccator. Five samples based on the Al/LiF/SiC/LiF system were prepared and measured in the 50-190 nm spectral range. These samples resulted in high reflective and narrowband coatings peaked at 100-101 nm, with a promising reflectance ratio Lyman β/Lyman α when fresh. Some efficiency degradation was observed after the sample storage in a desiccators; however all samples retained a narrowband performance over time and a high Lyman β/Lyman α ratio. The same system can be designed to be an efficient narrowband coating peaked in the target spectral range and not constrained to a specific performance at Lyman α. Hence an 8-month aged sample exhibited a reflectance as high as 61% at the peak wavelength of 100.9 nm, at near-normal incidence, the highest experimental reflectance reported in this range for a narrowband coating. We have also prepared narrowband transmission coatings tuned either at 135.6 nm or at the center of the LBH band (~160 nm), with the requirement to strongly reject the out-of-band, particularly the visible and close ranges. The coatings were based on (Al/MgF2)n multilayers, with n ranging between 3 and 4. The coatings were successful at rejecting the visible, with a transmittance lower than 10-5. The transmittance at the peak was 0.087 for coatings stored in a desiccators for 13 days.
Characterisation of low power readout electronics for a UV microchannel plate detector with cross-strip readout
M. Pfeifer,
J. Barnstedt,
S. Diebold,
et al.
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Astronomical observations in the ultraviolet (UV) wavelength range between 91 and 300nm are fundamental for the progress in astrophysics. Scientific success of future UV observatories raises the need for technology development in the areas of detectors, optical components, and their coatings. We develop solar blind and photon counting microchannel plate (MCP) UV detectors as a contribution to the progress in UV observation technology. New combinations of materials for the photocathode (see paper No. 9144-111, this volume, for details) as well as a cross-strip (XS) anode, having 64 strips on each layer, are used. Pre-amplification of the charge deposited onto the anode is performed by the Beetle chip designed at the Max-Planck-Institute for Nuclear Physics in Heidelberg for LHCb at CERN. It features 128 pre-amplifiers on one die and provides the analogue output in a four-fold serial stream. This stream is digitised by only four ADCs and is processed in an FPGA. This concept results in a reduced power consumption well below 10W as well as a reduced volume, weight and complexity of the readout electronics compared to existing cross-strip readouts. We developed an electronics prototype assembly and a setup in a vacuum chamber that is similar to the configuration in the final detector. The setup in the chamber is used for the burn-in of the MCPs as well as for tests of the readout electronics prototype assembly incorporating realistic signals. In this paper, information on the XS anodes as well as on the hybrid PCB carrying the Beetle pre-amplifier chip is shown. Details on the readout electronics design as well as details of the setup in the vacuum chamber are presented. An outlook to the next steps in the development process is given.
Performance characterization of UV science cameras developed for the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)
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The NASA Marshall Space Flight Center (MSFC) has developed a science camera suitable for sub-orbital missions for observations in the UV, EUV and soft X-ray. Six cameras will be built and tested for flight with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP), a joint National Astronomical Observatory of Japan (NAOJ) and MSFC sounding rocket mission. The goal of the CLASP mission is to observe the scattering polarization in Lyman-α and to detect the Hanle effect in the line core. Due to the nature of Lyman-α polarizationin the chromosphere, strict measurement sensitivity requirements are imposed on the CLASP polarimeter and spectrograph systems; science requirements for polarization measurements of Q/I and U/I are 0.1% in the line core. CLASP is a dual-beam spectro-polarimeter, which uses a continuously rotating waveplate as a polarization modulator, while the waveplate motor driver outputs trigger pulses to synchronize the exposures. The CCDs are operated in frame-transfer mode; the trigger pulse initiates the frame transfer, effectively ending the ongoing exposure and starting the next. The strict requirement of 0.1% polarization accuracy is met by using frame-transfer cameras to maximize the duty cycle in order to minimize photon noise. The CLASP cameras were designed to operate with ≤ 10 e-/pixel/second dark current, ≤ 25 e- read noise, a gain of 2.0 +- 0.5 and ≤ 1.0% residual non-linearity. We present the results of the performance characterization study performed on the CLASP prototype camera; dark current, read noise, camera gain and residual non-linearity.
UVMag: Space UV and visible spectropolarimetry
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UVMag is a project of a space mission equipped with a high-resolution spectropolarimeter working in the UV and visible range. This M-size mission will be proposed to ESA at its M4 call. The main goal of UVMag is to measure the magnetic fields, winds and environment of all types of stars to reach a better understanding of stellar formation and evolution and of the impact of stellar environment on the surrounding planets. The groundbreaking combination of UV and visible spectropolarimetric observations will allow the scientists to study the stellar surface and its environment simultaneously. The instrumental challenge for this mission is to design a high-resolution space spectropolarimeter measuring the full- Stokes vector of the observed star in a huge spectral domain from 117 nm to 870 nm. This spectral range is the main difficulty because of the dispersion of the optical elements and of birefringence issues in the FUV. As the instrument will be launched into space, the polarimetric module has to be robust and therefore use if possible only static elements. This article presents the different design possibilities for the polarimeter at this point of the project.
The soft x-ray photon-counting telescope for solar observations
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We present overview and development activities of a soft X-ray photon-counting spectroscopic imager for the solar corona that we conceive as a possible scientific payload for future space solar missions including Japanese Solar-C. The soft X-ray imager will employ a Wolter I grazing-incidence sector mirror with which images of the corona (1 MK to beyond 10 MK) will be taken with the highest-ever angular resolution (0.5"/pixel for a focal length of 4 m) as a solar Xray telescope. In addition to high-resolution imagery, we attempt to implement photon-counting capability for the imager by employing a backside-illuminated CMOS image sensor as the focal-plane device. Imaging-spectroscopy of the X-ray corona will be performed for the first time in the energy range from ~0.5 keV up to 10 keV. The imaging-spectroscopic observations with the soft X-ray imager will provide a noble probe for investigating mechanism(s) of magnetic reconnection and generation of supra-thermal (non-thermal) electrons associated with flares. Ongoing development activities in Japan towards the photon-counting imager is described with emphasis on that for sub-arcsecond-resolution grazing-incidence mirrors.
Current progress of optical alignment procedure of CLASP's Lyman-alpha polarimetry instrument
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The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a sounding-rocket instrument currently under development at the National Astronomical Observatory of Japan (NAOJ) as a part of an international collaboration. CLASP’s optics are composed of a Cassegrain telescope and a spectro-polarimeter which are designed to achieve an unprecedentedly accurate polarization measurement of the Ly-α line at 121.6nm emitted from the solar upper-chromosphere and transition region. CLASP’s first flight is scheduled for August 2015. Reaching such accuracy requires a careful alignment of the optical elements to optimize the image quality at 121.6 nm. However Ly-α is absorbed by air and therefore the optics alignment has to be done under vacuum condition which makes any experiment difficult. To bypass this issue, we proposed to align the telescope and the spectrograph separately in visible light. Hence we present our alignment procedure for both telescope and spectro-polarimeter. We will explain details about the telescope preliminary alignment before mirrors coating, which was done in April 2014, present the telescope combined optical performance and compare them to CLASP tolerance. Then we will present details about an experiment designed to confirm our alignment procedure for the CLASP spectro-polarimeter. We will discuss the resulting image quality achieved during this experiment and the lessons learned.
Hardware and software architecture on board solar orbiter/METIS: an update
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METIS, is one of the ten instruments selected to be part of the Solar Orbiter payload; it is a coronagraph that will investigate the inner part of the heliosphere performing imaging in the visible band and in the hydrogen Lyman α line @ 121.6 nm. METIS has recently undergone throughout a revision to simplify the instrument design. This paper will provide an overview of the updated hardware and software design of the coronagraph as presented at the Instrument Delta-Preliminary Design Review occurred in April 2014. The current configuration foresees two detectors, an Intensified APS for the UV channel and an APS for the visible light equipped with a Liquid Crystal Variable Retarder (LCVR) plate to perform broadband visible polarimetry. Each detector has a proximity electronics generating the control and readout signals for the sensor but the operations of the two devices are in charge of a centralized unit, the METIS Processing and Power Unit (MPPU). The MPPU operates the remaining electrical subsystems supplying them with power and providing on board storage and processing capabilities. Its design foresees the redundancy of the most critical parts, thus mitigating the effects of possible failures of the electronics subsystems. The central monitoring unit is also in charge of providing the communication with the S/C, handling the telemetry and telecommand exchange with the platform. The data acquired by the detectors shall undergo through a preliminary on-board processing to maximize the scientific return and to provide the necessary information to validate the results on ground. Operations as images summing, compression and cosmic rays monitoring and removal will be fundamental not only to mitigate the effects of the main sources of noise on the acquired data, but also to maximize the data volume to be transferred to the spacecraft in order to fully exploit the limited bandwidth telemetry downlink. Finally, being Solar Orbiter a deep-space mission, some METIS procedures have been designed to provide the instrument an efficient autonomous behavior in case of an immediate reaction is required as for the arising of transient events or the occurrence of safety hazards conditions.
Complex of instrumentation KORTES for the EUV and x-ray imaging and spectroscopy of the solar corona
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We report on the current status of the KORTES project – the first sun-oriented mission for the International Space Station to be launched in 2016-2017. KORTES will comprise several imaging and spectroscopic instruments that will observe solar corona in a number of wavebands, covering EUV and X-Ray ranges. A brief overview of the instrumentation of KORTES, its’ layout, technical parameters and scientific objectives is given. An additional attention is given to the design of multilayer optics and filters to be employed in EUV instruments of KORTES.
Solar simulation test up to 13 solar constants for the thermal balance of the Solar Orbiter EUI instrument
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Solar Orbiter EUI instrument was submitted to a high solar flux to correlate the thermal model of the instrument. EUI, the Extreme Ultraviolet Imager, is developed by a European consortium led by the Centre Spatial de Liège for the Solar Orbiter ESA M-class mission. The solar flux that it shall have to withstand will be as high as 13 solar constants when the spacecraft reaches its 0.28AU perihelion. It is essential to verify the thermal design of the instrument, especially the heat evacuation property and to assess the thermo-mechanical behavior of the instrument when submitted to high thermal load. Therefore, a thermal balance test under 13 solar constants was performed on the first model of EUI, the Structural and Thermal Model. The optical analyses and experiments performed to characterize accurately the thermal and divergence parameters of the flux are presented; the set-up of the test, and the correlation with the thermal model performed to deduce the unknown thermal parameters of the instrument and assess its temperature profile under real flight conditions are also presented.
The dual-gain 10 μm back-thinned 3kx3k CMOS-APS detector of the solar orbiter extreme UV imager
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The Extreme Ultraviolet Imager (EUI) on-board the Solar Orbiter mission will provide image sequences of the solar atmosphere at selected spectral emission lines in the extreme and vacuum ultraviolet.
For the two Extreme Ultraviolet (EUV) channels of the EUI instrument, low noise and radiation tolerant detectors with low power consumption and high sensitivity in the 10-40 nm wavelength range are required to achieve the science objectives.
In that frame, a dual-gain 10 μm pixel pitch back-thinned 1k x 1k Active Pixel Sensor (APS) CMOS prototype has been tested during the preliminary development phase of the instrument, to validate the pixel design, the expected EUV sensitivity and noise level, and the capability to withstand the mission radiation environment.
Taking heritage of this prototype, the detector architecture has been improved and scaled up to the required 3k x 3k array. The dynamic range is increased, the readout architecture enhanced, the power consumption reduced, and the pixel design adapted to the required stitching. The detector packaging has also been customized to fit within the constraints imposed by the camera mechanical, thermal and electrical boundaries. The manufacturing process has also been adapted and back-thinning process improved.
Once manufactured and packaged, a batch of sensors will undergo a characterization and calibration campaign to select the best candidates for integration into the instrument qualification and flight cameras.
The flight devices, within their cameras, will then be embarked on the EUI instrument, and be the first scientific APSCMOS detectors for EUV observation of the Sun.
Cross strip anode readouts for large format, photon counting microchannel plate detectors: developing flight qualified prototypes of the detector and electronics
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Photon counting microchannel plate (MCP) imagers have been the detector of choice for most UV astronomical missions over the last two decades (e.g. EUVE, FUSE, COS on Hubble etc.). Over this duration, improvements in the MCP laboratory readout technology have resulted in better spatial resolution (x10), temporal resolution (x1000) and output event rate (x100), all the while operating at lower gain (x 10) resulting in lower high voltage requirements and longer MCP lifetimes. One such technology is the parallel cross strip (PXS) readout. Laboratory versions of PXS electronics have demonstrated < 20 μm FWHM spatial resolution, count rates on the order of 2 MHz, and temporal resolution of ~ 1ns. In 2012 our group at U.C. Berkeley, along with our partners at the U. Hawaii, received a Strategic Astrophysics Technology grant to raise the TRL of the PXS detector and electronics from 4 to 6 by replacing most of the high powered electronics with application specific integrated circuits (ASICs) which will lower the power, mass and volume requirements of the PXS detector. We were also tasked to design and fabricate a "standard" 50mm square active area MCP detector incorporating these electronics that can be environmentally qualified for flight (temperature, vacuum, vibration). The first ASICs designed for this program have been fabricated and are undergoing testing. We present the latest progress on these ASIC designs and performance and show imaging results from the new 50 x 50 mm XS detector.
The new event analysis of the Fermi large area telescope
Carmelo Sgrò
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Since its launch on June 11, 2008 the Fermi Large Area Telescope (LAT) has been exploring the gamma-ray sky at energies from 20 MeV to over 300 GeV. Five years of nearly flawless operation allowed a constant improvement of the detector knowledge and, as a consequence, continuous update of the event selection and the corresponding instrument response parametrization. The final product of this effort is a radical revision of the entire event-level analysis, from the event reconstruction algorithms in each subsystem to the background rejection strategy. The potential improvements include a larger acceptance coupled with a significant reduction in background contamination, better angular and energy resolution and an extension of the energy reach below 100 MeV and in the TeV range. In this paper I will describe the new reconstruction and the event-level analysis, show the expected instrument performance and discuss future prospects for astro-particle physics with the LAT.
Calibration of the Compton Spectrometer and Imager in preparation for the 2014 balloon campaign
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The Compton Spectrometer and Imager (COSI) is a balloon-borne soft gamma-ray (0.2-5 MeV) telescope designed to perform wide-field imaging, high-resolution spectroscopy, and novel polarization measurements of astrophysical sources. COSI employs a compact Compton telescope design, utilizing 12 cross-strip germanium detectors to track the path of incident photons, where position and energy deposits from Compton interactions allow for a reconstruction of the source position in the sky, an inherent measure of the linear polarization, and significant background reduction. The instrument has recently been rebuilt with an updated and optimized design; the polarization sensitivity and effective area have increased due to a change in detector configuration, and the new lightweight gondola is suited to fly on ultra-long duration flights with the addition of a mechanical cryocooler system. COSI is planning to launch from the Long Duration Balloon site at McMurdo Station, Antarctica, in December 2014, where our primary science goal will be to measure gamma-ray burst (GRB) polarization. In preparation for the 2014 campaign, we have performed preliminary calibrations of the energy and 3-D position of interactions within the detector, and simulations of the angular resolution and detector efficiency of the integrated instrument. In this paper we will present the science goals for the 2014 COSI campaign and the techniques and results of the preliminary calibrations.
Monte Carlo simulations of gamma-ray space telescopes: a BoGEMMS multi-purpose application
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After the development of a BoGEMMS (Bologna Geant4 Multi-Mission Simulator) template for the background study of X-ray telescopes, a new extension is built for the simulation of a Gamma-ray space mission (e.g. AGILE, Fermi), conceived to work as a common, multi-purpose framework for the present and future electron tracking gamma-ray space telescopes. The Gamma-ray extension involves the Geant4 mass model, the physics list and, more important, the production and treatment of the simulation output. From the user point of view, the simulation set-up follows a tree structure, with the main level being the selection of the simulation framework (the general, X-ray or gamma-ray application) and the secondary levels being the detailed configuration of the geometry and the output format. The BoGEMMS application to Gamma-ray missions has been used to evaluate the instrument performances of a new generation of Gamma-ray telescopes (e.g. Gamma-Light), and a full simulation of the AGILE mission is currently under construction, to scientifically validate and calibrate the simulator with real in-space data sets. A complete description of the BoGEMMS Gamma-ray framework is presented here, with an overview of the achieved results for the potential application to present and future experiments (e.g., GAMMA-400 and Gamma-Light). The evaluation of the photon conversion efficiency to beta particle pairs and the comparison to tabulated data allows the preliminary physical validation of the overall architecture. The Gamma-ray module application for the study of the Gamma-Light instrument performances is reported as reference test case.
The x-ray timing and polarization satellite - 1, 2, 3: uncovering the mysteries of black holes and extreme physics in the universe
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The X-ray Timing and Polarization (XTP) satellite, planned for launch in ~2020, is dedicated to the study of 1- singularity (Black Hole), 2-stars (normal neutron star and magnetar) and 3-extremes (the physics under extreme gravity, density and magnetism). With an effective area of ~1 m2 and a combination of various types of X-ray telescopes, XTP is expected to make the most sensitive temporal and polarization observations with good energy resolution in 1-30 keV. XTP will open a new window using its powerful capability of polarization observations; its minimum detectable polarization will be 3% (1 mCrab, 1e6 s).
Current status of the GRAPE balloon program
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The Gamma RAy Polarimeter Experiment (GRAPE) was first own on a 26-hour balloon flight in the fall of 2011. GRAPE consists of an array of Compton polarimeter modules (based on traditional scintillation technologies) designed to operate in the energy range from 50 keV up to 500 keV. The ultimate goal of our program is to operate GRAPE in a wide FoV configuration for the study of gamma-ray bursts. For the first balloon flight, GRAPE was configured in a collimated mode to facilitate observations of known point sources. The Crab nebula/pulsar, the active Sun, and Cygnus X{1 were the primary targets for the first flight. Polarization results from this flight are summarized. Plans for the next GRAPE balloon flight, which is scheduled to take place in the fall of 2014 from Ft. Sumner, NM, will also be presented. These plans involve modifications designed to improve the polarization sensitivity, including an expansion of the array of polarimeter modules from 16 to 24 and improvements to the instrument shielding. These improvements to the instrument will significantly improve the polarization sensitivity, enabling a measurement of the Crab Nebula polarization to be made during the 2014 balloon flight.
Fifteen years of the Advanced CCD Imaging Spectrometer
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As the Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory enters its fifteenth year of operation on orbit, it continues to perform well and produce spectacular scientific results. The response of ACIS has evolved over the lifetime of the observatory due to radiation damage, molecular contamination and aging of the spacecraft in general. Here we present highlights from the instrument team’s monitoring program and our expectations for the future of ACIS. The ACIS calibration source produces multiple line energies and fully illuminates the entire focal plane which has greatly facilitated the measurement of charge transfer inefficiency and absorption from contamination. While the radioactive decay of the source has decreased its utility, it continues to provide valuable data on the health of the instrument. Performance changes on ACIS continue to be manageable, and do not indicate any limitations on ACIS lifetime.
Research on ICCD for space observation of cosmic ray and dark matter
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The low light level imaging and ultrafast detection system is a high performance ICCD composed of imaging intensifier and high-frame-rate CCD, the important readout system of the semi-digital 3D-imaging calorimeter for space observation of cosmic ray and dark matter that has the function of intensifying, delaying, imaging and memorizing, making rapid response to the ultrafast low light signals that is transmitted by tens of thousands of wavelength shifting fibers, generated by the semi-digital 3D-imaging calorimeter when cosmic ray is passing through. Using the images of ICCD and the semi-digital information reconstruction method, the particle type, energy and direction of cosmic ray can be obtained. By solving some key technologies such as coupling techniques of optical parts, low noise and high speed imaging of high-frame-rate and large-area CCD, the high speed gating system of imager intensifier, the prototype of high performance ICCD is developed. The prototype of ICCD can meet the requirements: up to 400 frames per second, detection ability for low light about 10 photons, linear dynamic range more than 300.Performances verification of the prototype is carried out by using a single photon test system. In this paper we will describe the requirement of ICCD for the ground cosmic detection system which is used to verify the theory of Herd (High Energy Cosmic-Radiation Detection), the key techniques used to achieve perfect performances, and test method and result of the ICCD.
Monte Carlo simulation of HERD calorimeter
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The High Energy cosmic-Radiation Detection (HERD) facility onboard China's Space Station is planned for operation starting around 2020 for about 10 years. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. The calorimeter plays an essential role in the main scientific objectives of HERD. A 3-D cubic calorimeter filled with high granularity crystals as active material is a very promising choice for the calorimeter. HERD is mainly composed of a 3-D calorimeter (CALO) surrounded by silicon trackers (TK) from all five sides except the bottom. CALO is made of 9261 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. Here the simulation results of the performance of CALO with GEANT4 and FLUKA are presented: 1) the total absorption CALO and its absorption depth for precise energy measurements (energy resolution: 1% for electrons and gammarays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV); 2) its granularity for particle identification (electron/proton separation power better than 10-5); 3) the homogenous geometry for detecting particles arriving from every unblocked direction for large effective geometrical factor (<3 m2sr for electron and diffuse gammarays, >2 m2sr for cosmic ray nuclei); 4) expected observational results such as gamma-ray line spectrum from dark matter annihilation and spectrum measurement of various cosmic ray chemical components.
The transition-edge EBIT microcalorimeter spectrometer
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The Transition-edge EBIT Microcalorimeter Spectrometer (TEMS) is a 1000-pixel array instrument to be delivered
to the Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory (LLNL)
in 2015. It will be the first fully operational array of its kind. The TEMS will utilize the unique capabilities of
the EBIT to verify and benchmark atomic theory that is critical for the analysis of high-resolution data from
microcalorimeter spectrometers aboard the next generation of x-ray observatories. We present spectra from the
present instrumentation at EBIT, as well as our latest results with time-division multiplexing using the current
iteration of the TEMS focal plane assembly in our test platform at NASA/GSFC.
Progress towards a double flux-locked-loop scheme for SQuID readout of TES detector arrays
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Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.
Performance improvement of x-ray CCDs by applying a magnetic field
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X-ray CCDs are widely used as the focal plane detectors of the X-ray telescopes. Among them, backside illuminated CCDs with a deep depletion layer are preferred because of their high quantum efficiency in both soft and hard X-ray bands. However, they tend to have poorer energy resolution and higher background due to the relatively large charge diffusion. We carried out simple experiments to apply a magnetic field of 0.25 T or 0.4 T to the CCD, which is expected to suppress the charge diffusion very slightly and to bring subtle improvement in the performance of the CCD. We found unexpectedly that grade branching ratios of Grade 3 and Grade 4, both are horizontal split events, symmetrically changed depending on the direction of the applied magnetic field. Although the cause of the change is not understand yet, it clearly demonstrate that the charge cloud in the CCD is affected by the externally applied magnetic field. We also found a decrease of Grade 7 only in the experiment 2. We consider this may be caused by the supress of the charge diffusion by the magnetic field, although other possibilities can not be excluded. No significant improvement was detected in the energy resolution. We could show with these experiments that the charge cloud in the CCD may be controlled by the externally applied magnetic field. Magnetic field may become useful tool in future to improve the performance of CCDs.
The use of Schottky CdTe detectors for high-energy astronomy: application to the detection plane of the instrument SVOM/ECLAIRs
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Ohmic CdZnTe and CdTe detectors have been successfully used in high-energy missions such as IBIS on-board INTEGRAL and the Swift-BAT in the past two decades. Such detectors provide very good quantum efficiency in the hard X-ray band. For the future generation of hard X-ray coded mask detectors, a higher sensitivity will be required. A way to achieve this is to increase the effective area of the pixilated detection plane, to change the mask pattern and/or the properties of the semi-conductors paving the detection plane. For the future Chinese-French Gamma-ray burst mission SVOM, the GRB trigger camera ECLAIRs will make use of a new type of high-energy detectors, the Schottky CdTe detectors. Such detectors, when reversely biased, are known to present very low leakage current, resulting in lower values of the low-energy threshold (down to 4 keV or less) than for previous missions (i.e. > 10 keV for the Swift-BAT and INTEGRAL/IBIS). Such low values will enable ECLAIRs with a moderate geometrical area of 1024 cm2 and a low-energy threshold of 4 keV to be more sensitive to high-redshift GRBs (emitting mainly in X-rays) than the Swift-BAT with a higher effective area and low-energy threshold. However, the spectral performance of such detectors are known to degrade over time, once polarized, due to the polarization effect that strongly depends on the temperature and the bias voltage applied to the detectors. In this paper, we present an intensive study of the properties of Schottky CdTe detectors as used on SVOM/ECLAIRs such as I-V characteristics, polarization effect, activation energy and low temperature annealing effects. We discuss the implications of these measurements on the use of this type of detectors in future high-energy instruments.
SuperHERO: the next generation hard x-ray HEROES telescope
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SuperHERO is a new high-resolution, Long Duration Balloon-capable, hard-x-ray (20-75 keV) focusing telescope for making novel astrophysics and heliophysics observations. The SuperHERO payload, currently in its proposal phase, is being developed jointly by the Astrophysics Office at NASA Marshall Space Flight Center and the Solar Physics Laboratory and the Wallops Flight Facility at NASA Goddard Space Flight Center. SuperHERO is a follow-on payload to the High Energy Replicated Optics to Explore the Sun (HEROES) balloon-borne telescope that recently flew from Fort Sumner, NM in September of 2013, and will utilize many of the same features. Significant enhancements to the HEROES payload will be made, including the addition of optics, novel solid-state multi-pixel CdTe detectors, integration of the Wallops Arc-Second Pointer and a significantly lighter gondola suitable for Long Duration Flights.
Preserving accurate figures in coating and bonding mirrors for lightweight x-ray telescopes
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Lightweight, high-resolution, high throughput optics for x-ray astronomy requires fabrication and integration of thin mirrors segments with arc-second precision. In this paper, we present results on our effort leading to the most recent two test modules achieving the intermediate goal of 10 arc-second resolution. We will address issues of coating and bonding thin glass mirrors with negligible distortion. Annealing of sputtered high-density metallic films was found to be sufficiently accurate. We will present result from tests of bonding mirrors onto experimental strongbacks, as well as the sensitivity on bonding procedure, bond parameters and environment.
Process of constructing a lightweight x-ray flight mirror assembly
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Lightweight and high resolution optics are needed for future space-based x-ray telescopes to achieve advances in highenergy astrophysics. NASA’s Next Generation X-ray Optics (NGXO) project has made significant progress towards building such optics, both in terms of maturing the technology for spaceflight readiness and improving the angular resolution. Technology Development Modules (TDMs) holding three pairs of mirrors have been regularly and repeatedly integrated and tested both for optical performance and mechanical strength. X-ray test results have been improved over the past year from 10.3 arc-seconds Half Power Diameter (HPD) to 8.3 arc-seconds HPD. A vibration test has been completed to NASA standard verification levels showing the optics can survive launch and pointing towards improvements in strengthening the modules through redundant bonds. A Finite Element Analysis (FEA) study was completed which shows the mirror distortion caused by bonding is insensitive to the number of bonds. Next generation TDMs, which will demonstrate a lightweight structure and mount additional pairs of mirrors, have been designed and fabricated. The light weight of the module structure is achieved through the use of E-60 Beryllium Oxide metal matrix composite material. As the angular resolution of the development modules has improved, gravity distortion during horizontal x-ray testing has become a limiting factor. To address this issue, a facility capable of testing in the vertical orientation has been designed and planned. Test boring at the construction site suggest standard caisson construction methods can be utilized to install a subterranean vertical vacuum pipe. This facility will also allow for the testing of kinematically mounted mirror segments, which greatly reduces the effect of bonding displacements. A development platform demonstrating the feasibility of kinematically mounting mirror segments has been designed, fabricated, and successfully tested.
Analysis of the optical surface properties in the indirect glass slumping
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The demand for larger collecting areas in X-ray telescopes within the mass limits of the launcher creates the need for light-weight mirror materials. At our institute we develop the technology of indirect thermal slumping of thin glass sheets to manufacture light mirror segments. A crucial part of the development is the measurement of the glass surface, shape and thickness profile in order to evaluate the quality of the reproduction method. We describe the measurement set-up, the analysis method of the surface profile and the evaluation of thickness variations in the glass, as well as their influence on the final glass sheets.
Mounting for fabrication, metrology, and assembly of full-shell grazing-incidence optics
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Future x-ray telescopes will likely require lightweight mirrors to attain the large collecting areas needed to accomplish the science objectives. Understanding and demonstrating processes now is critical to achieving sub-arcsecond performance in the future. Consequently, designs not only of the mirrors but of fixtures for supporting them during fabrication, metrology, handling, assembly, and testing must be adequately modeled and verified. To this end, MSFC is using finite-element modeling to study the effects of mounting on thin, full-shell grazing-incidence mirrors, during all processes leading to flight mirror assemblies. Here we report initial results of this study.
Fabrication of single crystal silicon mirror substrates for X-ray astronomical missions
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The advancement of X-ray astronomy largely depends on technological advances in the manufacturing of X-ray optics. Future X-ray astronomy missions will require thousands of nearly perfect mirror segments to produce an X-ray optical assembly with < 5 arcsecond resolving capability. Present-day optical manufacturing technologies are not capable of producing thousands of such mirrors within typical mission time and budget allotments. Therefore, efforts towards the establishment of a process capable of producing sufficiently precise X-ray mirrors in a time-efficient and cost-effective manner are needed. Single-crystal silicon is preferred as a mirror substrate material over glass since it is stronger and free of internal stress, allowing it to retain its precision when cut into very thin mirror substrates. This paper details our early pursuits of suitable fabrication technologies for the mass production of sub-arcsecond angular resolution single-crystal silicon mirror substrates for X-ray telescopes.
Alignment and integration of thin, lightweight x-ray optics into modules
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Future X-ray telescopes with high angular resolution and high throughput optics will help enable new high energy observations. X-ray optics in development at NASA Goddard Space Flight Center by the Next Generation X-ray Optics (NGXO) group utilizes a Flight Mirror Assembly (FMA) comprised of dozens of mirror modules populated with mirror segments aligned to a common focus. Mirror segments are currently aligned and permanently fixed into a module one at a time with emphasis on preventing degradation of the overall module performance. To meet cost and schedule requirements, parallelization and automation of the module integration process must be implemented. Identification of critical mirror segment alignment factors in addition to the progress towards a robust and automated module integration process is presented. There is a fundamental need for a reliable mirror segment alignment and bonding process that will be performed on hundreds or thousands of mirror segments. Results from module X-ray performance verification tests are presented to confirm module performance meets requirements.
Studies of lightweight x-ray telescope with CFRP
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We studies lightweight X-ray mirror with Carbon Fiber Reinforced Plastic (CFRP) substrate for next generation X-ray satellites.
CFRP is suitable material as substrate for thin-foil highly nested X-ray mirrors like telescope of Suzaku, ASTRO-H since it has properties of higher strength-to-weight ratio and flexibility of forming than that of metals.
In the current year we made flat panels for basic research and full/partial shell substrates by quasi-isotropic laminate with 8 ply prepregs, and performed reflector replication based on technique for the HXT mirror.
Industrialization scenario for X-ray telescopes production based on glass slumping
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Large X-ray segmented telescopes will be a key element for future missions aiming to solve still hidden mysteries of the hot and energetic Universe, such as the role of black holes in shaping their surroundings or how and why ordinary matter assembles into galaxies and clusters as it does. The major challenge of these systems is to guarantee a large effective area in combination with large field of view and good angular resolution, while maintaining the mass of the entire system within the geometrical and mass budget posed by space launchers. The slumping technology presents all the technical potentiality to be implemented for the realization of such demanding systems: it is based on the use of thin glass foils, shaped at high temperature in an oven over a suitable mould. Thousands of slumped segments are then aligned and assembled together into the optical payload. An exercise on the mass production approach has been conducted at Max Planck Institute for Extraterrestrial Physics (MPE) to show that the slumping technology can be a valuable approach for the realization of future X-ray telescopes also from a point of view of industrialization. For the analysis, a possible design for the ATHENA mission telescope was taken as reference.
Characterising x-ray mirror deformations with a phase measuring deflectometry system
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MPE is developing modular x-ray mirrors for the next generation of high-energy astronomy missions. The mirror segments are based on thermally formed (a.k.a. slumped) glass sheets, with a typical thickness of 400µm. One of the major challenges is the alignment and integration of the mirror segments and the associated metrology. The optical performance of the mirror can be significantly compromised by adhesive shrinkage, gravity sag or residual stresses influenced by the properties of the mirror mounting and the integration procedure. In parallel with classic coordinate measurement techniques we utilize a deflectometry based metrology system to characterization shape errors of the mirror surfaces. A typical deflectometry setup uses a TFT display to project a sinusoidal pattern onto a specular test surface (SUT) and a camera that observes the reflected image. This reflected image contains slope information of the SUT in the form of distortions of the original displayed pattern. A phase shifting technique can be used to recover this slope information with only very few exposures and reasonable computational effort. The deflectometry system enables us to characterize bonding interfaces of slumped glass mirrors, as well as influence of temporary mounting points, handling and thermal distortions. It is also well suited to measure transient effects.
Upgrade of the thirty-meter x-ray pencil beam line at the Institute of Space and Astronautical Science
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The thirty-meter X-ray pencil beam line at the Institute of Space and Astronautical Science (ISAS) was utilized for ground-based calibrations of X-ray telescopes (XRTs) onboard the ASTRO-D, the ASTRO-E and the ASTRO- E2 satellites. Recent upsizing or downsizing of XRT required upgrade of the ISAS beam line. We replaced a vacuum chamber in which the stages had been installed by a new cylindrical chamber whose diameter and length are 1.8 m and 11.3 m, respectively. Stages on which a telescope and detectors had been mounted were also replaced. At same time, a new CCD consists of 1240×1152 pixels whose size are 22.5×22.5 μm was introduced. The detector stage can be moved along the X-ray beam in the vacuum chamber, which allows us to change the distance between the sample and the detectors from 0.7 m to 9 m. The two stages can move in at least 500×500 mm2 of square in the plane normal to the X-ray beam. The pitching of some moving axes are measured at 60 arcsec at most. The others are no more than about 30 arcsec. From April 2013, the ASTRO-H Soft X-ray telescopes (SXTs) have been calibrated at the new ISAS beam line.
Alignment and integration of slumped glass x-ray mirrors at MPE
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This paper provides an update on the current activities for alignment and integration of slumped glass x-ray mirrors at MPE. Progress is being made w.r.t. the integration facility which is currently transitioned from a manual bench top setup to a full scale robotic system based on a high precision hexapod and collimated beam metrology. We present the most important design considerations and features of this new system as well as progress on other details of the integration concept.
A high resolution large x-ray mission based on thin glass: optomechanical design
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The technology of X-ray optics based on very thin glass sheets curved on mandrels figured to an optical quality have been quickly developed in these last years, as the on flight NUSTAR or the glass solutions for the IXO mission have demonstrated. Different possibilities to freeze the correct shape can be chosen and the constrains to the glass can widely affect the response in term of strength and quality. This study shows the opto-mechanical performances of the design based on the hot slumped glass sheets stiffed with reinforcing ribs. With this concept a glass stack can be integrated into a mechanical structure in order to form a module that can be assembled in a large structure. The considered input data and requirements are those specified for the proposed Athena mission. Different types of materials are considered following the latest progress in the slumping and the availability of alternative tougher glass. Static and dynamic FE analyses coupled with ray-tracing are performed in order to reach a high resolution (less than 5 arcsec). Also an optimization of the ribs distribution is implemented in function of the radius of curvature.
Shaping of thin glass X-ray telescope mirrors using air bearing slumping and ion implantation
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Air bearing glass slumping followed by ion implantation for fine figure correction constitutes a promising process for fabricating thin glass segmented mirrors for future high-resolution x-ray telescopes. We have previously demonstrated the feasibility of both air bearing slumping and ion implantation figure correction to produce mirrors with good figure and without introducing mid spatial-frequency errors or roughness. In this work, we describe a mechanically-robust slumping tool design that can be adapted to Wolter I mirror shapes; and we describe progress on understanding ion implantation for use as a figure correction process, by using in-situ curvature measurements in a tandem ion accelerator.
Ray tracing simulations for the wide-field x-ray telescope of the Einstein Probe mission based on Geant4 and XRTG4
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Einstein Probe (EP) is a proposed small scientific satellite dedicated to time-domain astrophysics working in the soft X-ray band. It will discover transients and monitor variable objects in 0.5-4 keV, for which it will employ a very large instantaneous field-of-view (60° × 60°), along with moderate spatial resolution (FWHM ∼ 5 arcmin). Its wide-field imaging capability will be achieved by using established technology in novel lobster-eye optics. In this paper, we present Monte-Carlo simulations for the focusing capabilities of EP’s Wide-field X-ray Telescope (WXT). The simulations are performed using Geant4 with an X-ray tracer which was developed by cosine (http://cosine.nl/) to trace X-rays. Our work is the first step toward building a comprehensive model with which the design of the X-ray optics and the ultimate sensitivity of the instrument can be optimized by simulating the X-ray tracing and radiation environment of the system, including the focal plane detector and the shielding at the same time.
Manufacture of aspherical molding dies for x-ray telescopes after ASTRO-H
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Producing X-ray imaging space telescopes is a very expensive endeavor, due in great part to the difficulty of fabricating thin mirrors for Wolter type-I optical assemblies. To meet this challenge, replication from optical molding dies (also called mandrels) has become the preferred method, as it is reliable and economical. Several replication methods exist: in the case of the ASTRO-H mission, DC magnetron sputtering was used to deposit Pt/C multilayer coating on glass molding dies. The multilayer coating was then bonded with epoxy to aluminum shells and then separated from the die. Another mirror replication method consists of slumping thin glass sheets over a full (or a section of) revolution molding die under high temperature. This method was demonstrated in the case of the NuSTAR mission.
But the challenge of fabricating truly aspheric Wolter type molding dies, which are capable of highly accurate angular resolution (below 5 arcs), remains very expensive and time consuming. In this paper, three methods for producing X-ray optic molding dies are presented. Each method uses a different substrate material and process chain, as follows: electroless nickel plated aluminum (first diamond turned then correctively polished), fused silica (first precision ground then correctively polished), and CVD silicon carbide (which can be finished entirely with a newly developed Shape Adaptive Grinding process). The process chains employed for each method are explained in details, and their relative merits discussed. A way forward for the next generation of X-ray telescopes after ASTRO-H is then drawn out.
Enhanced far-ultraviolet reflectance of MgF2 and LiF over-coated Al mirrors
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This paper presents and discuss data obtained on a distribution of Al+MgF2 and Al+LiF witness coupons that show substantial gains in reflectance in the far-ultraviolet (FUV) part of the optical spectrum (90−180 nm). These samples, which have dimensions of 2×2 inches, were coated at various locations inside a 2−me diameter coating chamber at the Goddard Space Flight Center in Greenbelt, MD (USA). These experiments were done to demonstrate a scale−up process for coating up to a 1−m diameter optic, and hence realize the gain in throughput that could be obtained for a telescope system that would employ such mirror coatings. These coatings have been optimized for Lyman-alpha (121.6 nm) or lower wavelengths and they are prepared with the deposition of the MgF2 or LiF layers done at elevated (∼ 250 °C) temperature. These results will be compared to ambient or “cold” depositions. We will also present optical characterization of little-studied rare-earth fluorides, such as GdF3 and LuF3, that exhibit low absorption over a broad wavelength range and could therefore be used as high-index materials to produce dielectric coatings at FUV wavelengths.
Recent developments and results of new ultraviolet reflective mirror coatings
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Astronomical observations in the Lyman–ultraviolet (91 – 122 nm) are limited in part by the performance of reflective coatings. Currently, the best reflective mirror options for the UV wavelength range of 90 -122 nm are LiF+Al (R ~ 60% from 102 – 200 nm) and SiC (R ~ 30 % from 90 – 200 nm). Higher reflectivity coatings in the 90 – 122 nm range will improve sensitivity and allow for more complex instrumentation. We are working to develop, laboratory test and eventually space test new reflective UV coatings (R > 70% from 90 – 115 nm) that also preserve high-reflectivity performance (R > 80% from 115 – 800 nm) throughout the longer-wavelength vacuum ultraviolet and visible spectral bands. We present a progress report on our work with new protective thin film deposition techniques of metal fluorides (MgF2 and AlF3) on high intrinsic broadband reflective metal (aluminum) surfaces. We present first test results from both traditional and atomic layer deposition processes. In this paper, we discuss the current status of the deposition process, coating substrates, reflectivity measurements for optical through far-ultraviolet wavelengths as well as environmental storage sensitivities.
Data acquisition system and ground calibration of polarized gamma-ray observer (PoGOLite)
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The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object between the energy-range 25–80 keV in one 6 hour flight. Polarization measurements in soft gamma-rays are expected to provide a powerful probe into high-energy emission mechanisms in/around neutron stars, black holes, supernova remnants, active-galactic nuclei etc. The “pathfinder” flight was performed in July 2013 for 14 days from Sweden to Russia. The polarization is measured using Compton scattering and photoelectric absorption in an array of 61 well-type phoswich detector cells (PDCs) for the pathfinder instrument. The PDCs are surrounded by 30 BGO crystals which form a side anti-coincidence shield (SAS) and passive polyethylene neutron shield. There is a neutron detector consisting of LiCaAlF6 (LiCAF) scintillator covered with BGOs to measure the background contribution of atmospheric neutrons. The data acquisition system treats 92 PMT signals from 61 PDCs + 30 SASs + 1 neutron detector, and it is developed based on SpaceWire spacecraft communication network. Most of the signal processing is done by digital circuits in Field Programmable Gate Arrays (FPGAs). This enables the reduction of the mass, the space and the power consumption. The performance was calibrated before the launch.
The development of gamma-ray burst polarimeter for a small satellite
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We are developing a gamma-ray burst polarimeter for a small satellite. It is Compton-scattering-type polarimeter which consists of segmented plastic scintillator and segmented GAGG scintillator. The scattering position in the plastic scintillator and the absorption position in the GAGG scintillator for incident hard X rays can be read out by multi-anode photomultipliers and avalanche photodiodes, respectively. The detection efficiency and the modulation factor amount to about 21% and 39% at 60 keV, respectively. The geometrical area for one module is about 300 cm2. If two modules will be installed, the polarimeters will measure the polarization for about thirty-five GRBs in two years. Through the observation of the polarization, the radiation mechanism of gamma-ray bursts will be clarified.
Simulation studies on performance parameters of a TPC polarimeter
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X-ray polarimeters based on Time Projection Chamber (TPC) geometry are currently being studied and developed to make sensitive measurement of polarization in 2-10keV energy range. TPC soft X-ray polarimeters exploit the fact that emission direction of the photoelectron ejected via photoelectric effect in a gas proportional counter carries the information of the polarization of the incident X-ray photon. Operating parameters such as pressure, drift field and driftgap affect the performance of a TPC polarimeter. Simulations presented here showcase the effect of these operating parameters on the modulation factor of the TPC polarimeter. Models of Garfield are used to study photoelectron interaction in gas and drift of electron cloud towards Gas Electron Multiplier (GEM). The emission direction is reconstructed from the image and modulation factor is computed. Our study has shown that Ne/DME (50/50) at lower pressure and drift field can be used for a TPC polarimeter with modulation factor of 50-65%.
Monte-Carlo estimation of the inflight performance of the GEMS satellite x-ray polarimeter
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We report a Monte-Carlo estimation of the in-orbit performance of a cosmic X-ray polarimeter designed to be installed on the focal plane of a small satellite. The simulation uses GEANT for the transport of photons and energetic particles and results from Magboltz for the transport of secondary electrons in the detector gas. We validated the simulation by comparing spectra and modulation curves with actual data taken with radioactive sources and an X-ray generator. We also estimated the in-orbit background induced by cosmic radiation in low Earth orbit.
Performance verification of the Gravity and Extreme Magnetism Small explorer (GEMS) x-ray polarimeter
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Polarimetry is a powerful tool for astrophysical observations that has yet to be exploited in the X-ray band. For satellite-borne and sounding rocket experiments, we have developed a photoelectric gas polarimeter to measure X-ray polarization in the 2–10 keV range utilizing a time projection chamber (TPC) and advanced micro-pattern gas electron multiplier (GEM) techniques. We carried out performance verification of a flight equivalent unit (1/4 model) which was planned to be launched on the NASA Gravity and Extreme Magnetism Small Explorer (GEMS) satellite. The test was performed at Brookhaven National Laboratory, National Synchrotron Light Source (NSLS) facility in April 2013. The polarimeter was irradiated with linearly-polarized monochromatic X-rays between 2.3 and 10.0 keV and scanned with a collimated beam at 5 different detector positions. After a systematic investigation of the detector response, a modulation factor ≥35% above 4 keV was obtained with the expected polarization angle. At energies below 4 keV where the photoelectron track becomes short, diffusion in the region between the GEM and readout strips leaves an asymmetric photoelectron image. A correction method retrieves an expected modulation angle, and the expected modulation factor, ~20% at 2.7 keV. Folding the measured values of modulation through an instrument model gives sensitivity, parameterized by minimum detectable polarization (MDP), nearly identical to that assumed at the preliminary design review (PDR).
Properties of the flight model gas electron multiplier for the GEMS mission
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We present the gain properties of the gas electron multiplier (GEM) foil in pure dimethyl ether (DME) at 190 Torr. The GEM is one of the micro pattern gas detectors and it is adopted as a key part of the X-ray polarimeter for the GEMS mission. The X-ray polarimeter is a time projection chamber operating in pure DME gas at 190 Torr. We describe experimental results of (1) the maximum gain the GEM can achieve without any discharges, (2) the linearity of the energy scale for the GEM operation, and (3) the two-dimensional gain variation of the active area. First, our experiment with 6.4 keV X-ray irradiation of the whole GEM area demonstrates that the maximum effective gain is 2 x 104 with the applied voltage of 580 V. Second, the measured energy scale is linear among three energies of 4.5, 6.4, and 8.0 keV. Third, the two-dimensional gain mapping test derives the standard deviation of the gain variability of 7% across the active area.
Development of CCDs for REXIS on OSIRIS-REx
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The Regolith x-ray Imaging Spectrometer (REXIS) is a coded-aperture soft x-ray imaging instrument on the OSIRIS-REx spacecraft to be launched in 2016. The spacecraft will fly to and orbit the near-Earth asteroid Bennu, while REXIS maps the elemental distribution on the asteroid using x-ray fluorescence. The detector consists of a 2×2 array of backilluminated 1k×1k frame transfer CCDs with a flight heritage to Suzaku and Chandra. The back surface has a thin p+-doped layer deposited by molecular-beam epitaxy (MBE) for maximum quantum efficiency and energy resolution at low x-ray energies. The CCDs also feature an integrated optical-blocking filter (OBF) to suppress visible and near-infrared light. The OBF is an aluminum film deposited directly on the CCD back surface and is mechanically more robust and less absorptive of x-rays than the conventional free-standing aluminum-coated polymer films. The CCDs have charge transfer inefficiencies of less than 10-6, and dark current of 1e-/pixel/second at the REXIS operating temperature of –60 °C. The resulting spectral resolution is 115 eV at 2 KeV. The extinction ratio of the filter is ~1012 at 625 nm.
Effect of a magnetic field generated by permanent magnets on the GPD polarization sensitivity
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The Gas Pixel Detector (GPD) is an imaging X-ray polarimeter with a moderate spectral resolution and a very good position resolution.1, 2 The GPD derives this information from the true 2-d charge image of the photoelectron track produced in gas and collected by an ASIC CMOS chip after its drift and its multiplication. In this paper we report on the experimental results of the study of the effect of a strong magnetic field in reducing the diffusion and increasing the sensitivity for a GPD filled with one bar of He-DME 20-80. We generated a magnetic field of about 1600 Gauss by means of commercial magnets made of an alloy of Neodymium-Iron-Boron configured as one ring and one cylinder. We compared the pixel size distributions and the modulation curves with and without magnets at two different drift fields, corresponding to different nominal diffusion properties, with both polarized and unpolarized sources. The results obtained show that a not sensitive improvement is present at this fields implying that a much larger magnetic field is necessary with this mixture, albeit a shift on the position angle of the modulation curve, derived from a polarized source, is observed.
The new SCOS-based EGSE of the EPIC flight-spare on-ground cameras
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The XMM-Newton observatory, launched by the European Space Agency in 1999, is still one of the scientific community’s most important high-energy astrophysics missions. After almost 15 years in orbit its instruments continue to operate smoothly with a performance close to the immediate post-launch status. The competition for the observing time remains very high with ESA reporting a very healthy over-subscription factor. Due to the efficient use of spacecraft consumables XMM-Newton could potentially be operated into the next decade. However, since the mission was originally planned for 10 years, progressive ageing and/or failures of the on-board instrumentation can be expected. Dealing with them could require substantial changes of the on-board operating software, and of the command and telemetry database, which could potentially have unforeseen consequences for the on-board equipment. In order to avoid this risk, it is essential to test these changes on ground, before their upload. To this aim, two flight-spare cameras of the EPIC experiment (one MOS and one PN) are available on-ground. Originally they were operated through an Electrical Ground Support Equipment (EGSE) system which was developed over 15 years ago to support the test campaigns up to the launch. The EGSE used a specialized command language running on now obsolete workstations. ESA and the EPIC Consortium, therefore, decided to replace it with new equipment in order to fully reproduce on-ground the on-board configuration and to operate the cameras with SCOS2000, the same Mission Control System used by ESA to control the spacecraft. This was a demanding task, since it required both the recovery of the detailed knowledge of the original EGSE and the adjustment of SCOS for this special use. Recently this work has been completed by replacing the EGSE of one of the two cameras, which is now ready to be used by ESA. Here we describe the scope and purpose of this activity, the problems faced during its execution, the adopted solutions, and the tests performed to demonstrate the effectiveness of the new EGSE.
The eROSITA x-ray baffle
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The X-ray baffle is an important part of the eROSITA mirror assembly as it reduces the stray light caused by single reflections at the Wolter 1 Mirrors by more than 90%. The stray light problem and possible solutions were analyzed by ray-tracing resulting in a trade-off between effective stray light protection and avoidance of vignetting. Possible design alternatives were considered and the influences of manufacturing tolerances were studied. Other than for XMM, the eROSITA X-ray baffle could not be realized as sieve plates; instead a system of co-aligned “baffle rings” was mounted onto each of the mirror modules. The mechanical design is based on concentric Invar foils fixed by an own spider. The complete X-ray baffles were finally mounted to the mirror module while the alignment was controlled by optical means.
A setup for soft proton scattering on x-ray mirrors
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Protons with energies between tens of keV and some MeV can degrade the performance of X-ray detectors and contribute to the instrument background. In-orbit measurements showed that the flux of soft protons funneled through Wolter-type mirrors is considerably larger than expected from simulations. Up to now, just very few results from laboratory experiments have been reported and the data is not sufficient to pinpoint the best analytical description of the physical process or to validate simulation codes. In order to improve this situation, a small angle scattering experiment to measure the proton reflection properties of X-ray mirrors has been set up at the accelerator facility of the University of Tübingen. The experimental setup and initial preliminary results obtained with samples of eROSITA mirror shells are presented.
ART-XC/SRG: results of thermo-vacuum tests
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ART-XC – a medium-x-ray-energy survey instrument for SRG project is being developed in Russia. Space Research institute (IKI) and Federal Nuclear Center (VNIIEF) has developed and tested the STM (Structural and Thermal Model) of ART-XC/SRG Instrument. The STM was tested in a 40 m3 vacuum chamber, equipped with black cryogenic screens, cooled by liquid nitrogen. During the tests various thermal telescope modes were simulated. In particular we have simulated emergency mode, when mirrors heaters were switched-off. During the tests temperature of instrument’s structure was controlled by 64 independent sensors. Stability of optical axis of mirror systems was also measured. STM test has shown that temperature of mirror system was lower than required, temperature of detectors met the requirements. The test also confirmed geometrical stability of the carbon fiber housing despite of significant temperature gradients. Additional experiments with two mirror systems, each containing a full set of simple nickel shells, were performed. In these experiments we have measured longitudinal and transverse temperature gradients of mirror systems. Next thermovacuum tests of the qualification model of the ART-XC instrument are being prepared. Results of STM tests are presented in this paper.
The calibration of flight mirror modules for the ART-XC instrument on board the SRG mission
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MSFC is fabricating x-ray optics for the Astronomical Roentgen Telescope – X-Ray Concentrator (ART-XC or ART for short) instrument under agreements with the Russian Space Research Institute (IKI). ART-XC is one of two instruments that will be launched on the Russian-German Spectrum-Roentgen-Gamma (SRG) Mission to be launched in 20161. Delivery of the flight optics for ART-XC (7 mirror modules) is currently scheduled for summer/fall of 20142. MSFC has to date completed assembly of four modules and has performed extensive calibration on two of these. These calibrations show that the modules meet effective area requirements and greatly exceed the angular resolution requirements. Details of the calibration procedure and an overview of the results obtained to date are presented here.
Analysis of proton propagation through the eROSITA telescope
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The German telescope eROSITA will be the first X-ray instrument orbiting around the L-2 lagrangian point. Therefore, modelling the radiation environment in that region of space and its interaction with the instrument is particularly important, as no measured data of other X-ray detectors can be used as a reference to predict how the space conditions will impact the instrumental capabilities. The orbit around L-2 extends well beyond the Earth´s magnetosphere, where the flux of galactic cosmic particles is cut by the geomagnetic field, and fluxes of energetic particles one order of magnitude higher than in low Earth orbits are expected. Furthermore, as experienced by Chandra and XMM-Newton, softer protons may be scattered through the mirror shells and funneled to the focal plane, representing a potential additional source of background. To investigate and assess this component we are developing a ray tracing simulator for protons, that follows the track of each proton from the entrance pupil down to the focal plane. As a first step of analysis, we report here the estimate of the proton reflection efficiency for the eROSITA mirror shells obtained using a dataset of reflectivity parameters for Gold based on TRIM simulations.
Bumber filter against micrometeoroids for eROSITA
E. Perinati,
S. Bugiel,
M. Freyberg,
et al.
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The German X-ray telescope eROSITA will perform the first imaging all-sky survey in the medium energy range up to 10 keV with unprecedented spectral and angular resolution. The launch of eROSITA onboard of the Russian Spectrum- Röntgen-Gamma satellite into an orbit around the L-2 lagrangian point is foreseen in 2016. Even tough the L-2 space environment can be considered free of orbital debris, the presence of extraterrestrial meteoroids in the interplanetary space implies a certain hazard for the eROSITA pnCCDs, as experienced by both pn and MOS cameras onboard XMM-Newton. In this paper we address this question and investigate the response of the optical blocking filter to hypervelocity impacts.
The x-ray telescope eROSITA: qualification of the thermal control system
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eROSITA is the core instrument on the Spektrum-Röntgen-Gamma (SRG) mission, scheduled for launch in 2016. The main tasks of the thermal control system are heating of the mirror modules, cooling of the camera electronics, cooling of the CCD detectors and temperature control of the telescope structure in general. Special attention is paid to the camera cooling, since it is the most critical one. The complex assembly with the sevenfold symmetry of the eROSITA telescope requires an innovative design. Large distances and a very low operating temperature (–90°C to –100°C) place high demands on the cooling chain. In total, three different types of low-temperature ethane heat pipes are used to transport the heat from the cameras to two radiators outside the telescope structure. Extreme environmental temperature gradients with the Sun on the one side and the cold space on the other present a real challenge not only to the camera cooling systems, but to the overall thermal control. A thermal model of the complete telescope was used to predict the thermal behavior of the telescope and its subsystems. Through various tests, this model could be improved step by step. The most complex test was the space simulation test of the eROSITA qualification model in January 2013 at the IABG facilities in Ottobrunn, Germany. About 50 heaters, a liquid-nitrogen-cooled chamber and a Sun simulator provided realistic mission conditions. Approximately 200 temperature sensors monitored the relevant temperatures during the test. The results were predominantly within the predicted intervals and therefore not only verified the complete concept but also enabled a further refining of the thermal model. This, in turn, allows for reliable predictions of the thermal behavior during the mission. Some deviations required minor changes in the final design which were implemented and re-qualified in a separate test of the thermal control system flight model in March 2014 in the PANTER test facility of MPE. The results of both tests will be presented in this contribution.
Arcus: an ISS-attached high-resolution x-ray grating spectrometer
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We present the design and scientific motivation for Arcus, an X-ray grating spectrometer mission to be deployed on the International Space Station. This mission will observe structure formation at and beyond the edges of clusters and galaxies, feedback from supermassive black holes, the structure of the interstellar medium and the formation and evolution of stars. The mission requirements will be R>2500 and >600 cm2 of effective area at the crucial O VII and O VIII lines, values similar to the goals of the IXO X-ray Grating Spectrometer. The full bandpass will range from 8-52Å (0.25-1.5 keV), with an overall minimum resolution of 1300 and effective area >150 cm2. We will use the silicon pore optics developed at cosine Research and proposed for ESA’s Athena mission, paired with off-plane gratings being developed at the University of Iowa and combined with MIT/Lincoln Labs CCDs. This mission achieves key science goals of the New Worlds, New Horizons Decadal survey while making effective use of the International Space Station (ISS).
The camera of the Microchannel X-ray telescope onboard the SVOM mission
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The Microchannel X-Ray Telescope will be implemented on board the SVOM space mission to observe the afterglow of gamma-ray bursts and localize them with 2 arcmin precision. The optical system is based on microchannel plates assembling in Wolter-I configuration to focus the X-rays in the focal plane, like done for the MIXS telescope of the BepiColombo ESA mission. The sensor part is a 256 × 256 pixel pnCCD from the Max-Planck Institute for Extraterrestrial Physics for high resolution spectroscopy and high quantum efficiency over 0.2 – 10 keV energy range, based on the same technology and design as the eROSITA telescopes for the Russian-German SRG mission. CEA-Irfu (Saclay) is in charge of the design and the realization of the camera, including the focal plane, the calibration wheel, the front-end electronics, the structure housing for background shielding and the active cooling system. A prototype of the full detection chain and the acquisition system was set up. The paper presents the preliminary design of the electrical, mechanical and thermal architectures of the camera. It focuses on the fabrication and testing of the critical elements of the design and concludes on the on-going developments.
ECLAIRs detection plane: current state of development
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ECLAIRs, a 2-D coded-mask imaging camera on-board the Sino-French SVOM space mission, will detect and locate Gamma-ray bursts (GRBs) in near real time in the 4-150 keV energy band. The design of ECLAIRs has been mainly driven by the objective of achieving a low-energy threshold of 4 keV, unprecedented for this type of instrument. The detection plane is an assembly of 6400 Schottky CdTe semiconductor detectors of size 4x4x1 mm3 organized on elementary hybrid matrices of 4x8 detectors. The detectors will be polarized from -300V to -500V and operated at -20°C to reduce both the leakage current and the polarization effect induced by the Schottky contact. The remarkable low-energy threshold homogeneity required for the detection plane has been achieved thanks to: i) an extensive characterization and selection of the detectors, ii) the development of a specific low-noise 32-channel ASIC, iii) the realization of an innovative hybrid module composed of a thick film ceramic (holding 32 CdTe detectors with their high voltage grid), associated to an HTCC ceramic (housing the ASIC chip within an hermetic enclosure). In this paper, we start describing a complete hybrid matrix, and then the manufacturing of a first set of 50 matrices (representing 1600 detectors, i.e. a quarter of ECLAIRs detector’s array). We show how this manufacturing allowed to validate the different technologies used for this hybridization, as well as the industrialization processes. During this phase, we systematically measured the leakage current on Detector Ceramics after an outgassing, and the Equivalent Noise Charge (ENC) for each of the 32 channels on ASIC Ceramics, in order to optimize the coupling of the two ceramics. Finally, we performed on each hybrid module, spectral measurements at -20°C in our vacuum chamber, using several calibrated radioactive sources (241Am and 55Fe), to check the performance homogeneity of the 50 modules. The results demonstrated that the 32-detector hybrid matrices presented homogeneous spectral properties and that a lowenergy threshold of 4 keV for each detector could be reached. In conclusion, our hybrid module has obtained the performance required at the SVOM mission level and successfully withstood the space environment tests (TRL 6/7). This development phase has given us the opportunity to build a detector’s array prototype (Engineering Model) equipped with 50 hybrid modules. Thanks to this prototype we are in the process of validating a complete detection chain (from the detectors to the backend electronics) and checking the performance. In addition it enables us to consolidate the instrument’s mechanical and thermal design, and to write preliminary versions of the quality procedures required for integration, functional tests and calibration steps. At the end of this prototype development and testing, we will be ready to start the detailed design of the detection plane Flight Model.
Engineering design of the Regolith X-ray Imaging Spectrometer (REXIS) instrument: an OSIRIS-REx student collaboration
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OSIRIS-REx is a NASA New Frontiers mission scheduled for launch in 2016 that will travel to the asteroid Bennu and return a pristine sample of the asteroid to Earth. The REgolith X-ray Imaging Spectrometer (REXIS) is a student collaboration instrument on-board the OSIRIS-REx spacecraft. REXIS is a NASA risk Class D instrument, and its design and development is largely student led. The engineering team consists of MIT graduate and undergraduate students and staff at the MIT Space Systems Laboratory. The primary goal of REXIS is the education of science and engineering students through participation in the development of light hardware. In light, REXIS will contribute to the mission by providing an elemental abundance map of the asteroid and by characterizing Bennu among the known meteorite groups. REXIS is sensitive to X-rays between 0.5 and 7 keV, and uses coded aperture imaging to map the distribution of iron with 50 m spatial resolution. This paper describes the science goals, concept of operations, and overall engineering design of the REXIS instrument. Each subsystem of the instrument is addressed with a high-level description of the design. Critical design elements such as the Thermal Isolation Layer (TIL), radiation cover, coded-aperture mask, and Detector Assembly Mount (DAM) are discussed in further detail.
The x-ray facilities in-building for calibrations of HXMT
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Calibration is one of the key issues for the Hard X-ray Modulation Telescope (HXMT) on board the first Chinese astronomical satellite. As its core sciences are to observe the Galactic X-ray binaries, transients and the diffuse X-ray emission, the corresponding calibration tasks are mainly about the energy response and the effective area. To this end we are building two facilities specified to the calibration needs of the three scientific payloads of HXMT: the high energy telescope (HE), the medium energy telescope (ME) and the low energy telescope (LE). By adopting a double crystal monochromator, the X-ray beam can be extracted with an intrinsic energy dispersion of well below 1%. The light spot is limited to a size of a few mm under the constraints of the length of the facility which is about 6 m, and of the requirement on the intrinsic energy dispersion which is less than 1%. The HE facility was accomplished in 2013 and the LE/ME facility will be available in the middle of 2014.
The Canadian Astro-H Metrology System
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The Hard X-ray Telescopes on Astro-H have a 12-meter focal length. In order to achieve this long focal length and still fit compactly in the H-IIA launch fairing, the detectors are mounted at the end of an extendable optical bench that will be deployed in orbit. Once in operation, the spacecraft will experience distortions primarily due to thermal fluctuations in low-earth orbit and it is important that the misalignment between the telescopes and instruments is accurately measured. The Canadian Astro-H Metrology System (CAMS) is a laser alignment system that will measure optical alignment deviations. The CAMS is compact, consumes little power, and is stable over a wide temperature range. The system will be used to measure lateral (X/Y) displacement as well as rotational shifts in the optical bench. In addition, the CAMS data can be used to enhance the quality of the hard X-ray images that will have been degraded by structural deformations. A description of the CAMS hardware and the relevant data processing algorithms are provided.
Recent progress in the ground calibration of the ASTRO-H Hard X-ray telescope (HXT-2)
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The 6th Japanese X-ray satellite, ASTRO-H, equips two Hard X-ray Telescopes (HXTs) to perform imaging spectroscopy up to 70 keV. The 2nd flight module (HXT-2) had been completed in July, 2013. After some environmental tests were passed, the X-ray performance of the HXT-2 was measured at the SPring-8 BL20B2, 3rd generation synchrotron facility. The angular resolution defined with a Half Power Diameter (HPD) was 1:′9 at 30 keV and 1:′8 at 50 keV. This small energy dependence is considered to be caused by the difference in image quality of each foil; the inner mirror shells have better quality than outer ones. The effective area was found to be 178 cm2 at 30 keV and 82 cm2 at 50 keV, both of which exceed the requirement. Furthermore, the detailed energy dependence of the effective area was examined for a limited aperture in the 30{70 keV band with a pitch of 1 keV. We also measured the off-axis dependence of the effective area at 50 keV, and then determined the optical axis. The field of view of the HXT-2 was found to be 5:′6 (FWHM of the vignetting function), consistent with the simulation. In this paper, we also report the detailed analysis of the ground calibration data, which will be used for image reconstruction by a ray-tracing simulator.
Ground-based x-ray calibration of the Astro-H soft x-ray telescopes
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The X-ray astronomy satellite Astro-H, planned to be launched in 2015, will have several instruments for covering a wide energy band from a few hundreds eV to 600 keV. There are four X-ray telescopes, and two of them are soft X-ray telescopes (SXTs) covering up to about 15 keV. One is for an X-ray micro-calorimeter detector (SXS) and the other is for an X-ray CCD detector (SXI). The design of the SXTs is a conical approximation of the Wolter Type-I optics, which is also adopted for the telescopes on the previous mission Suzaku launched in 2005. It consists 203 thin-foil reflectors coated with gold monolayer (2000 Å) on the aluminum substrate (101.6 mm length) with the thickness of 0.15, 0.23 and 0.31 mm. These are nested confocally within the radius of 58 to 225 mm. The focal length of SXTs is 5.6 m. The weight is as light as ~ 43 kg per telescope.
We present the current status of the calibration activity of two SXTs (SXT-1 and SXT-2). The developments of two SXTs were completed by NASA's Goddard Space Flight Center (GSFC). First X-ray measurements with a diverging beam at the GSFC 100m beamline found an angular resolution at 8.0 keV to be 1.1 and 1.0 arcmin (HPD) for SXT-1 and SXT-2, respectively. The full characterization of the X-ray performance has been now continuously calibrated with the 30m X-ray beamline facility at the Institute of Space and Astronautical Science (ISAS) of Japan Aerospace eXploration Agency (JAXA) in Japan. We adopted a raster scan method with a narrow X-ray pencil beam with the divergence of ~ 15". X-ray characterization of the two SXTs has been measured from May and December 2013, respectively.
In the case of SXT-1, the on-axis effective area was approximately 580, 445, 370, 270, 185 and 90 cm2 at energies of 1.5, 4.5, 8.0, 9.4, 11.1 and 12.9 keV respectively. The effective area of SXT-2 is 2% larger than that of SXT-1 irrespective to X-ray energy. The on-axis angular resolution of SXT-1 was evaluated as 1.3 - 1.5 arcmin (HPD) in the 1.5 - 13 keV band. The resolution was slightly got worse at higher energies by ~ 0:3 arcmin. Otherwise, the resolution of SXT-2 is 1.2 arcmin, almost irrespective to X-ray energy. The field of view (FOV) was ~ 16 arcmin at 1.5 keV, decreasing with increasing X-ray energy, and became ~ 8 arcmin at 13 keV. The FOV is defined here as the full-width at half-maximum (FWHM) of the vignetting curve.
The X-ray performance of SXT-1 and SXT-2 meets the system requirements. Because all the parameters of the SXT-2 is slightly better that of SXT-1, we adopted the SXT-2 telescope for the SXS detector of the Astro-H primary instrument with the narrow FOV.
Revealing a detailed performance of the soft x-ray telescopes of the ASTRO-H mission
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The international X-ray observatory, ASTRO-H is currently planed as launched in 2015. The ASTRO-H mission covers a wide energy range from a few hundreds eV to 600 keV. The two Soft X-ray Telescopes (SXT- 1 and SXT-2) play a role to image the soft X-ray sky up to ~12 keV in that range. Each of them focuses an image on the focal plane detectors of the CCD camera (SXI) and the calorimeter (SXS-XCS), respectively. In this paper, we present spot scan measurements of the two SXTs. The spot scan fully illuminates the telescope by mapping with the 8 mm by 8 mm beam and creates the ”maps” of the half power diameter (HPD) and the focal location of the focused image. We found variations of performance at local area of the telescope. Each of the spot images has different focal-location and different HPD. Moreover, we found that the map of the HPD is very similar from quadrant to quadrant, but the map of the focal location is different from quadrant to quadrant, from radius to radius, and from azimuthal angle to angle.
Performance verification and system integration tests of the pulse shape processor for the soft x-ray spectrometer onboard ASTRO-H
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The soft X-ray spectrometer (SXS) aboard ASTRO-H is equipped with dedicated digital signal processing units called pulse shape processors (PSPs). The X-ray microcalorimeter system SXS has 36 sensor pixels, which are operated at 50 mK to measure heat input of X-ray photons and realize an energy resolution of 7 eV FWHM in the range 0.3–12.0 keV. Front-end signal processing electronics are used to filter and amplify the electrical pulse output from the sensor and for analog-to-digital conversion. The digitized pulses from the 36 pixels are multiplexed and are sent to the PSP over low-voltage differential signaling lines. Each of two identical PSP units consists of an FPGA board, which assists the hardware logic, and two CPU boards, which assist the onboard software. The FPGA board triggers at every pixel event and stores the triggering information as a pulse waveform in the installed memory. The CPU boards read the event data to evaluate pulse heights by an optimal filtering algorithm. The evaluated X-ray photon data (including the pixel ID, energy, and arrival time information) are transferred to the satellite data recorder along with event quality information. The PSP units have been developed and tested with the engineering model (EM) and the flight model. Utilizing the EM PSP, we successfully verified the entire hardware system and the basic software design of the PSPs, including their communication capability and signal processing performance. In this paper, we show the key metrics of the EM test, such as accuracy and synchronicity of sampling clocks, event grading capability, and resultant energy resolution.
Soft x-ray transmission of contamination blocking filter for SXI onboard ASTRO-H
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X-ray CCD operated onboard satellite are contaminated by outgas from organic material used in satellites. This contamination causes a significant reduction in the detection sensitivity of X-ray detectors.
In order to prevent such contamination to the Back-Illuminated CCD (BI-CCD) of the Soft X-ray Imager
(SXI) onboard ASTRO-H, we have developed a Contamination Blocking Filter (CBF), which consists of ~30nm thick Aluminum and ~200nm thick Polyimide. The CBF is be placed on the top of the CCD camera hood and is required to have a high X-ray transmission in order to take advantage of the high detection efficiency of BI-CCD.
We measured the X-ray transmission of three flight candidates of the CBF last October at the SPring-8 and obtained the X-ray transmission of three CBFs in the soft X-ray energy from 0.2 to 1.8 keV which covers the absorption edges around C-K, N-K, O-K, and Al-K including X-ray absorption fine structure (XAFS). In these measurements, we found three CBFs have high X-ray transmission below 2ke V, e.g. ~70% at around 0.5 keV, and determined the thickness of Al and Polyimide to be 220 nm and ~50 nm, respectively. We will calculate the response function of SXI including these results.
Thermal design of the hard x-ray imager and the soft gamma-ray detector onboard ASTRO-H
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The Hard X-ray Imager and the Soft Gamma-ray Detector, onboard the 6th Japanese X-ray satellite ASTRO-H, aim at unprecedentedly-sensitive observations in the 5–80 keV and 40–600 keV bands, respectively. Because their main sensors are composed of a number of semi-conductor devices, which need to be operated in a temperature of –20 to –15◦C, heat generated in the sensors must be efficiently transported outwards by thermal conduction. For this purpose, we performed thermal design, with the following three steps. First, we additionally included thermally-conductive parts, copper poles and graphite sheets. Second, constructing a thermal mathematical model of the sensors, we estimated temperature distributions in thermal equilibria. Since the model had rather large uncertainties in contact thermal conductions, an accurate thermal dummy was constructed as our final step. Vacuum measurement with the dummy successfully reduced the conductance uncertainties. With these steps, we confirmed that our thermal design of the main sensors satisfies the temperature requirement.
Development and calibration of fine collimators for the ASTRO-H Soft Gamma-ray Detector
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The Soft Gamma-ray Detector (SGD) is a Si/CdTe Compton telescope surrounded by a thick BGO active shield and is scheduled to be onboard the ASTRO-H satellite when it is launched in 2015. The SGD covers the energy range from 40 to 600 keV with high sensitivity, which allows us to study nonthermal phenomena in the universe. The SGD uses a Compton camera with the narrow field-of-view (FOV) concept to reduce the non-Xray background (NXB) and improve the sensitivity. Since the SGD is essentially a nonimaging instrument, it also has to cope with the cosmic X-ray background (CXB) within the FOV. The SGD adopts passive shields called “fine collimators” (FCs) to restrict the FOV to ≤ 0.6° for low-energy photons (≤ 100 keV), which reduces contamination from CXB to less than what is expected due to NXB. Although the FC concept was already adopted by the Hard X-ray Detector onboard Suzaku, FCs for the SGD are about four times larger in size and are technically more difficult to operate. We developed FCs for the SGD and confirmed that the prototypes function as required by subjecting them to an X-ray test and environmental tests, such as vibration tests. We also developed an autocollimator system, which uses visible light to determine the transmittance and the optical axis, and calibrated it against data from the X-ray test. The acceptance tests of flight models started in December 2013: five out of six FCs were deemed acceptable, and one more unit is currently being produced. The activation properties were studied based on a proton-beam test and the results were used to estimate the in-orbit NXB.
Development and verification of signal processing system of BGO active shield onboard Astro-H
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The hard X-ray imager (HXI) and soft gamma-ray detector (SGD) onboard Astro-H observe astronomical objects with high sensitivity in the hard X-ray (5−80 keV) and soft gamma-ray (40−600 keV) energy bands. To achieve this high sensitivity, background rejection is essential, and these detectors are surrounded by large and thick bismuth germinate scintillators as an active shield. We have developed adequate trigger logic for both the HXI and SGD to process signals from main detector and BGO shield simultaneously and then we optimized the trigger delay and width, with consideration of the trigger latch efficiency. The shield detector system performs well, even after it is assembled as the HXI sensor. The energy threshold maintains the same level as that observed during the prototype development phase, and the experimental room background level of the main detector is successfully reduced by our optimized trigger timing.
An expanded x-ray beam facility (BEaTriX) to test the modular elements of the ATHENA optics
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Future large X-ray observatories like ATHENA will be equipped with very large optics, obtained by assembling modular optical elements, named X-ray Optical Units (XOU) based on the technology of either Silicon Pore Optics or Slumped Glass Optics. In both cases, the final quality of the modular optic (a 5 arcsec HEW requirement for ATHENA) is determined by the accuracy alignment of the XOUs within the assembly, but also by the angular resolution of the individual XOU. This is affected by the mirror shape accuracy, its surface roughness, and the mutual alignment of the mirrors within the XOU itself. Because of the large number of XOUs to be produced, quality tests need to be routinely done to select the most performing stacked blocks, to be integrated into the final optic. In addition to the usual metrology based on profile and roughness measurements, a direct measurement with a broad, parallel, collimated and uniform Xray beam would be the most reliable test, without the need of a focal spot reconstruction as usually done in synchrotron light. To this end, we designed the BEaTriX (Beam Expander Testing X-ray facility) to be realized at INAF-OAB, devoted to the functional tests of the XOUs. A grazing incidence parabolic mirror and an asymmetrically cut crystal will produce a parallel X-ray beam broad enough to illuminate the entire aperture of the focusing elements. An X-ray camera at the focal distance from the mirrors will directly record the image. The selection of different crystals will enable to test the XOUs in the 1 - 5 keV range, included in the X-ray energy band of ATHENA (0.2-12 keV). In this paper we discuss a possible BEaTriX facility implementation. We also show a preliminary performance simulation of the optical system.
Studying ATHENA optics with divergent and collimated x-ray beams
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An open question in the measurement of X-ray optics for satellite experiments is what the PSF (point spread function) looks like in orbit and what the focal length for a source at infinite distance is. In order to measure segmented optics as proposed for ATHENA a collimated X-ray beam with a size of several square centimeters is necessary. We showed that by using a zone plate such a collimated beam can be achieved. We discuss here the requirements such a zone plate collimator has to comply in order to characterize with this collimator an ATHENA type optic. Additional we can present results obtained with a first version of such a collimator and can show so the proof of principle.
Optical design for ATHENA X-ray telescope based on slumped mirror segments
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The Hot and Energetic Universe will be the focus of future ESA missions: in late 2013 the theme was selected for the second large-class mission in the Cosmic Vision science program. Fundamental questions on how and why ordinary matter assemble into galaxies and clusters, and how black holes grow and influence their surroundings can be addressed with an advanced X-ray observatory. The currently proposed ATHENA mission presents all the potentiality to answer the outstanding questions. It is based on the heritage of XMM-Newton and on the previous studies for IXO mission. The scientific payload will require state of the art instrumentations. In particular, the baseline for the X-ray optical system, delivering a combination of large area, high angular resolution, and large field of view, is the Silicon Pore Optics technology (SPO) developed by ESA in conjunction with the Cosine Measurement Systems. The slumping technology is also under development for the manufacturing of future X-ray telescopes: for several years the Max Planck Institute for Extraterrestrial physics (MPE) has been involved in the analysis of the indirect slumping approach, which foresees the manufacturing of segmented X-ray shells by shaping thin glass foils at high temperatures over concave moulds so to avoid any contact of the optical surface with other materials during the process, preserving in this way the original X-ray quality of the glass surface. The paper presents an alternative optical design for ATHENA based on the use of thin glass mirror segments obtained through slumping.
VERITAS 2.0 a multi-channel readout ASIC suitable for the DEPFET arrays of the WFI for Athena
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VERITAS 2.0 is a multi-channel readout ASIC for pnCCDs and DEPFET arrays. The main chip application is the readout of the DEPFET pixel arrays of the Wide Field Imager for the Athena mission. Every readout channel implements a trapezoidal weighting function and it is based on a fully differential architecture. VERITAS 2.0 is the first ASIC able to readout the DEPFETs both in source follower mode and in drain current mode. The drain readout should make it possible to achieve a processing time of about 2-3 μs/line with an electronics noise ≤ 5 electrons r.m.s.. The main concept and first measurements are presented.
Towards Mo/Au based TES detectors for Athena/X-IFU
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The X-ray spectroscopy telescope Athena has been designed to implement the science theme "the hot and energetic universe", selected by the European Space Agency as the second large mission of its Cosmic Vision program. X-IFU, one of the two interchangeable focal plane instruments of Athena, is a high resolution X-ray spectrometer made of a large array of Transition Edge Sensors. Two options are under consideration for the X-IFU microcalorimeters: Ti/Au bilayers or Mo/Au bilayers. Here we report on our efforts to develop Mo/Au-based TES. The TES are made of high quality superconducting Mo/Au bilayers fabricated at room temperature on low stress Si3N4 membranes; Mo is deposited by RF magnetron sputtering and in-situ covered by a thin (15nm) Au layer deposited by DC sputtering; in a second step, the Au layer thickness is increased ex-situ by e-beam deposition, to obtain suitable resistance Rn and operation temperature values. Very sharp transitions (~few mK transition width) are obtained, with typically Rn~25mΩ and Tc~ 100-120mK for 65/215 bilayers. First simple TES designs are being tested. Also, Bi films several μm thick, intended to constitute the X-ray absorber, are fabricated by electrochemical deposition.
Requirements for the detectors and read-out of ATHENA X-IFU
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The detector system of the X-Ray Integral Field Unit (X-IFU), one of the two ATHENA focal plane instruments will be an ambitious step forward in the field of astronomical X-ray detection. We describe its baseline configuration, consisting of 3840 Transition Edge Sensors (TES) microcalorimeters with an energy resolution of 2.5 eV FWHM, spanning a 5 arcminute field-of-view and allowing an imaging resolution of 5 arcsec. The detectors are read out in 96 channels of 40 pixels each, using frequency domain multiplexing (FDM). Each channel contains a dual-stage SQUID pre-amplifier and a low-noise amplifier (LNA). In order to enhance the dynamic range of the SQUIDs a specific technique, baseband feedback (BBFB), is applied. The generation of the carrier and feedback signals, and the signal processing are done in the digital domain. We review the requirements for the main elements of this system, needed to ensure the high performance of the detector system. From the resolution requirements for the detectors follows a budget for contributions to the energy resolution on top of the intrinsic detector resolution. This budget forms the basis for the assessment of the dynamic range requirements for the SQUID and the LNA and the DACs and the ADC. Requirements are also derived for the levels of crosstalk and non-linearity in the readout chain.
TES-detector based focal plane assembly key-technology developments for ATHENA and SAFARI
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SRON, Netherlands Institute for Space Research, is developing a Focal Plane Assembly for future missions requiring large-format arrays of Transition Edge Sensors. The up-scaling of the amount of pixels together with the mass and volume limitations for a space instrument requires technology developments in several areas. A dedicated program has been initiated to develop the required magnetic shielding, high density electrical interconnects and a thermal insulating suspension. The purpose of the program is to demonstrate Technology Readiness Level 4-5 for these key-technologies before the end of 2015. In this talk we will present the status of the program, as carried out under ESA GSTP.
The Cryogenic AntiCoincidence detector for ATHENA: the progress towards the final pixel design
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“The Hot and Energetic Universe” is the scientific theme approved by the ESA SPC for a Large mission to be flown in the next ESA slot (2028th) timeframe. ATHENA is a space mission proposal tailored on this scientific theme. It will be the first X-ray mission able to perform the so-called “Integral field spectroscopy”, by coupling a high-resolution spectrometer, the X-ray Integral Field Unit (X-IFU), to a high performance optics so providing detailed images of its field of view (5’ in diameter) with an angular resolution of 5” and fine energy-spectra (2.5eV@E<7keV). The X-IFU is a kilo-pixel array based on TES (Transition Edge Sensor) microcalorimeters providing high resolution spectroscopy in the 0.2-12 keV range. Some goals is the detection of faint and diffuse sources as Warm Hot Intergalactic Medium (WHIM) or galaxies outskirts. To reach its challenging scientific aims, it is necessary to shield efficiently the X-IFU instrument against background induced by external particles: the goal is 0.005 cts/cm^2/s/keV. This scientific requirement can be met by using an active Cryogenic AntiCoincidence (CryoAC) detector placed very close to X-IFU (~ 1 mm below). This is shown by our GEANT4 simulation of the expected background at L2 orbit. The CryoAC is a TES based detector as the X-IFU sharing with it thermal and mechanical interfaces, so increasing the Technology Readiness Level (TRL) of the payload. It is a 2x2 array of microcalorimeter detectors made by Silicon absorber (each of about 80 mm^2 and 300 μm thick) and sensed by an Ir TES. This choice shows that it is possible to operate such a detector in the so-called athermal regime which gives a response faster than the X-IFU (< 30 μs), and low energy threshold (above few keV). Our consortium has developed and tested several samples, some of these also featured by the presence of Al-fins to efficiently collect the athermal phonons, and increased x-ray absorber area (up to 1 cm^2). Here the results of deep test related to one of the last sample produced (namely AC-S5), and steps to reach the final detector design will be discussed.
The DRE: the digital readout electronics for ATHENA X-IFU
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We are developing the digital readout electronics (DRE) of the X-Ray Integral Field Unit (X-IFU), one of the two Athena focal plane instruments. This subsystem is made of two main parts: the DRE-DEMUX and the DRE-EP. With a frequency domain multiplexing (FDM) the DRE-DEMUX makes the readout of the 3 840 Transition Edge Sensors (TES) in 96 channels of 40 pixels each. It provides the AC signals to voltage-bias the TES, it demodulates the detector's data which are readout by a SQUID and low noise amplifiers and it linearizes the detection chain to increase its dynamic range. The feedback is computed with a specific technique, so called baseband feedback (BBFB) which ensures that the loop is stable even with long propagation and processing delays (i.e. a few μs) and with high frequency AC-bias (up to 5 MHz). This processing is partly analogue (anti aliasing and reconstruction filters) but mostly digital. The digital firmware is simultaneously applied to all the pixels in digital integrated circuits. After the demultiplexing the interface between the DRE-DEMUX and the DRE-EP has to cope with a data rate of 61.44 Gbps to transmit the data of the individual pixels. Then, the DRE-EP detects the events and computes their energy and grade according to their spectral quality: low resolution, medium resolution and high resolution (i.e. if two consecutive events are too close the estimate of the energy is less accurate). This processing is done in LEON based processor boards. At its output the DRE-EP provides the control unit of the instrument with a list including for each event its time of arrival, its energy, its location on the focal plane and its grade.
Baseline design of the thermal blocking filters for the X-IFU detector on board ATHENA
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ATHENA is an advanced X-ray observatory designed by a large European consortium to address the science theme "Hot and Energetic Universe" recently selected by ESA for L2 – the second Large-class mission within the Cosmic Vision science program (launch scheduled in 2028). One of the key instruments of the mission is the X-ray Integral Field Unit (X-IFU), an array of Transition Edge Sensor (TES) micro-calorimeters with high energy resolution (2.5 eV @ 6 keV) in the energy range 0.2÷12 keV, operating at the focal plane of a large effective area high angular resolution (5" HEW) grazing incidence X-ray telescope.
The X-IFU operates at temperatures below 100 mK and thus requires a sophisticated cryostat. In order to allow the beam focused by the telescope to reach the X-IFU detector, windows need to be opened on the cryostat thermal and structural shields surrounding the cold stage. X-ray transparent thermal blocking filters need to be mounted on such open windows to make the radiation heat-load onto the detector array negligible with respect to conduction heat load and dissipated electrical power, and to minimize photon shot noise onto the detector. After a brief survey of the heritage from space satellite and sounding rocket experiments on thermal filters operated at cryogenic temperatures, we present the selected baseline design of the thermal filters for the ATHENA X-IFU detector, show the performances, and finally discuss possible improvements in the design to increase the X-IFU quantum efficiency at low energies.
The X-IFU operates at temperatures below 100 mK and thus requires a sophisticated cryostat. In order to allow the beam focused by the telescope to reach the X-IFU detector, windows need to be opened on the cryostat thermal and structural shields surrounding the cold stage. X-ray transparent thermal blocking filters need to be mounted on such open windows to make the radiation heat-load onto the detector array negligible with respect to conduction heat load and dissipated electrical power, and to minimize photon shot noise onto the detector. After a brief survey of the heritage from space satellite and sounding rocket experiments on thermal filters operated at cryogenic temperatures, we present the selected baseline design of the thermal filters for the ATHENA X-IFU detector, show the performances, and finally discuss possible improvements in the design to increase the X-IFU quantum efficiency at low energies.
ATHENA X-IFU detector cooling chain
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The TES (Transition Edge Sensors) micro-calorimeter detector technology in the X-IFU instrument for ATHENA (Astrophyics of the Hot and Energetic universe - Europe’s next generation X-ray observatory ATHENA) will require cooling down to 50 mK, and a stable and quiet Electro-Magnetic and micro-vibrations environment. In order to achieve this temperature and environment, a cooling chain integrated in a compact cryostat with an optimized electromagnetic environment has to be developed. Critical technology developments are covered, such as mechanical cryocoolers, support structures, radiative and EMC shields, micro-vibrations reduction, and others.
Coolers development for the ATHENA X-IFU cryogenic chain
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The hot and energetic universe has been selected by ESA as the science theme for the L2 mission with a planned launch in 2028. The Athena mission is one the potential mission concept for the next X-rays generation satellite. One of the instruments of this mission is the X-ray Integral Field Unit (X-IFU) which provides spatially resolved high resolution spectroscopy. This low temperature instrument requires high detector sensitivity that can only be achieved using 50 mK cooling. To obtain this temperature level, a careful design of the cryostat and of the cooling chain comprising different stages in cascade is needed. CEA has undertaken development in various areas to contribute to this cryochain including pulse tube coolers and sub-Kelvin coolers. This paper will describe the status of our different cooler developments. High temperature two stage pulse tube can be used for thermal shields cooling, 15 K pulse tube cooler for 2 K JT precooling and 4 K pulse tube cooler for a potential direct cooling of the sub-kelvin cooler. The 50 mK temperature is achieved using a sub-kelvin cooler comprising an adsorption cooler linked to an ADR stage. This elegant solution gives way to a light, compact and reliable cooler which has been validated in the SPICA/SAFARI project. Modified solutions are also under study to accommodate alternative design.
ATHENA end-to-end simulations
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We present an overview of the development of the end-to-end simulation programs for the instruments on the future European X-ray astronomy mission Athena. The overview includes the design considerations behind the simulation software and the current status and planned developments of the simulators for the X-ray Integral Field Unit and the Wide Field Imager.
Background studies for ATHENA: towards a new assessment phase
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In view of the endorsement of ATHENA as the future large space mission to explore the Hot and Energetic Universe scientific theme recently selected by ESA, we summarize here some aspects of the interplanetary radiation environment that will require further investigation in the new phase of assessment studies of background and radiation damage for the ATHENA focal plane instrumentation.
Development of the hard x-ray monitor onboard WF-MAXI
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WF-MAXI is a mission to detect and localize X-ray transients with short-term variability as gravitational-wave (GW) candidates including gamma-ray bursts, supernovae etc. We are planning on starting observations by WF-MAXI to be ready for the initial operation of the next generation GW telescopes (e.g., KAGRA, Advanced LIGO etc.). WF-MAXI consists of two main instruments, Soft X-ray Large Solid Angle Camera (SLC) and Hard X-ray Monitor (HXM) which totally cover 0.7 keV to 1 MeV band. HXM is a multi-channel array of crystal scintillators coupled with APDs observing photons in the hard X-ray band with an effective area of above 100 cm2. We have developed an analog application specific integrated circuit (ASIC) dedicated for the readout of 32-channel APDs' signals using 0.35 μm CMOS technology based on Open IP project and an analog amplifier was designed to achieve a low-noise readout. The developed ASIC showed a low-noise performance of 2080 e- + 2.3 e-/pF at root mean square and with a reverse-type APD coupled to a Ce:GAGG crystal a good FWHM energy resolution of 6.9% for 662 keV -rays.
Development of soft x-ray large solid angle camera onboard WF-MAXI
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Wide-Field MAXI (WF-MAXI) planned to be installed in Japanese Experiment Module “Kibo” Exposed Facility of the international space station (ISS). WF-MAXI consists of two types of cameras, Soft X-ray Large Solid Angle Camera (SLC) and Hard X-ray Monitor (HXM). HXM is multi-channel arrays of CsI scintillators coupled with avalanche photodiodes (APDs) which covers the energy range of 20 - 200 keV. SLC is arrays of CCD, which is evolved version of MAXI/SSC. Instead of slit and collimator in SSC, SLC is equipped with coded mask allowing its field of view to 20% of all sky at any given time, and its location determination accuracy to few arcminutes. In older to achieve larger effective area, the number of CCD chip and the size of each chip will be larger than that of SSC. We are planning to use 59 x 31 mm2 CCD chip provided by Hamamatsu Photonics. Each camera will be quipped with 16 CCDs and total of 4 cameras will be installed in WF-MAXI. Since SLC utilize X-ray CCDs it must equip active cooling system for CCDs. Instead of using the peltier cooler, we use mechanical coolers that are also employed in Astro-H. In this way we can cool the CCDs down to -100C. ISS orbit around the earth in 90 minutes; therefore a point source moves 4 arcminutes per second. In order to achieve location determination accuracy, we need fast readout from CCD. The pulse heights are stacked into a single row along the vertical direction. Charge is transferred continuously, thus the spatial information along the vertical direction is lost and replaced with the precise arrival time information. Currently we are making experimental model of the camera body including the CCD and electronics for the CCDs. In this paper, we show the development status of SLC.
Development of the Four-stage X-ray telescope (FXT) for the DIOS mission
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A Four-stage X-ray Telescope (FXT) has been developed as the best-fit optics for the Diffuse Intergalactic Oxygen Surveyor (DIOS) mission, a small satellite mission for mapping observations of the warm-hot intergalactic medium. The FXT mirrors are based on a conical approximation of the Wolter-I design, fabrication technique used in the Suzaku satellite. We made the second FXT demonstration model, in which we installed 4 sets of 4 stage mirrors with diameter of about 500 mm using alignment plate. Both optical and X-ray measurement were done to estimate FXT performance. Although angular resolution is two to three times worse than that of the requirement and the goal, the field of view and the effective area are consistent with expected performance derived by the ray tracing simulation.
Optimisation of the design for the LOFT large area detector module
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The Large Observatory For X-ray Timing (LOFT) is one of the 5 missions considered by ESA as an M3 candidate. The LOFT scientific payload consists of a collimated Large Area Detector (LAD) and a Wide Field Monitor (WFM).
The scale of the LAD (10 m² effective area) puts it in a new design space for X-ray astronomy, with resulting implications for design trade-offs, modularity, manufacturing, assembly, test and calibration processes. This paper focuses on the LAD module, which is the building block of the instrument. We present the overall module design, discussing these challenges and how they have been addressed.
The SIRIUS mixed analog-digital ASIC developed for the LOFT LAD and WFM instruments
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We report on the development and characterization of the low-noise, low power, mixed analog-digital SIRIUS ASICs for both the LAD and WFM X-ray instruments of LOFT. The ASICs we developed are reading out large area silicon drift detectors (SDD). Stringent requirements in terms of noise (ENC of 17 e- to achieve an energy resolution on the LAD of 200 eV FWHM at 6 keV) and power consumption (650 μW per channel) were basis for the ASICs design. These SIRIUS ASICs are developed to match SDD detectors characteristics: 16 channels ASICs adapted for the LAD (970 microns pitch) and 64 channels for the WFM (145 microns pitch) will be fabricated. The ASICs were developed with the 180nm mixed technology of TSMC.
Radiation tests of the silicon drift detectors for LOFT
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During the three years long assessment phase of the LOFT mission, candidate to the M3 launch opportunity of the ESA Cosmic Vision programme, we estimated and measured the radiation damage of the silicon drift detectors (SDDs) of the satellite instrumentation. In particular, we irradiated the detectors with protons (of 0.8 and 11 MeV energy) to study the increment of leakage current and the variation of the charge collection efficiency produced by the displacement damage, and we “bombarded” the detectors with hypervelocity dust grains to measure the effect of the debris impacts. In this paper we describe the measurements and discuss the results in the context of the LOFT mission.
Hyper-velocity impact test and simulation of a double-wall shield concept for the Wide Field Monitor aboard LOFT
E. Perinati,
M. Rott,
A. Santangelo,
et al.
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The space mission LOFT (Large Observatory For X-ray Timing) was selected in 2011 by ESA as one of the candidates for the M3 launch opportunity. LOFT is equipped with two instruments, the Large Area Detector (LAD) and the Wide Field Monitor (WFM), based on Silicon Drift Detectors (SDDs). In orbit, they would be exposed to hyper-velocity impacts by environmental dust particles, which might alter the surface properties of the SDDs. In order to assess the risk posed by these events, we performed simulations in ESABASE2 and laboratory tests. Tests on SDD prototypes aimed at verifying to what extent the structural damages produced by impacts affect the SDD functionality have been performed at the Van de Graaff dust accelerator at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. For the WFM, where we expect a rate of risky impacts notably higher than for the LAD, we designed, simulated and successfully tested at the plasma accelerator at the Technical University in Munich (TUM) a double-wall shielding configuration based on thin foils of Kapton and Polypropylene. In this paper we summarize all the assessment, focussing on the experimental test campaign at TUM.
Baseline design of the filters for the LAD detector on board LOFT
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The Large Observatory for X-ray Timing (LOFT) was one of the M3 missions selected for the phase A study in the ESA's Cosmic Vision program. LOFT is designed to perform high-time-resolution X-ray observations of black holes and neutron stars. The main instrument on the LOFT payload is the Large Area Detector (LAD), a collimated experiment with a nominal effective area of ~10 m2 @ 8 keV, and a spectral resolution of ~240 eV in the energy band 2-30 keV. These performances are achieved covering a large collecting area with more than 2000 large-area Silicon Drift Detectors (SDDs) each one coupled to a collimator based on lead-glass micro-channel plates. In order to reduce the thermal load onto the detectors, which are open to Sky, and to protect them from out of band radiation, optical-thermal filter will be mounted in front of the SDDs. Different options have been considered for the LAD filters for best compromise between high quantum efficiency and high mechanical robustness. We present the baseline design of the optical-thermal filters, show the nominal performances, and present preliminary test results performed during the phase A study.
The digital data processing concepts of the LOFT mission
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The Large Observatory for X-ray Timing (LOFT) is one of the five mission candidates that were considered by ESA for an M3 mission (with a launch opportunity in 2022 - 2024). LOFT features two instruments: the Large Area Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m2-class instrument with approximately 15 times the collecting area of the largest timing mission so far (RXTE) for the first time combined with CCD-class spectral resolution. The WFM will continuously monitor the sky and recognise changes in source states, detect transient and bursting phenomena and will allow the mission to respond to this. Observing the brightest X-ray sources with the effective area of the LAD leads to enormous data rates that need to be processed on several levels, filtered and compressed in real-time already on board. The WFM data processing on the other hand puts rather low constraints on the data rate but requires algorithms to find the photon interaction location on the detector and then to deconvolve the detector image in order to obtain the sky coordinates of observed transient sources. In the following, we want to give an overview of the data handling concepts that were developed during the study phase.
Instrumental and scientific simulations of the LOFT wide field monitor
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The Large Observatory for X-ray Timing (LOFT) is one of the five candidates that were considered by ESA as an M3 mission (with launch in 2022-2024). It is specifically designed to exploit the diagnostics of very rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. The LOFT scientific payload is composed of the Large Area Detector (LAD), devoted to spectral-timing observation, and the Wide Field Monitor (WFM), whose primary goal it is to monitor the X-ray sky for transient events that need to be followed up with the LAD, and to measure the long-term variability of galactic X-ray sources and localize gamma-ray bursts. Here we describe the simulations carried out to optimize the WFM design and to characterize the instrument response to both isolated sources and crowded fields in the proximity of the galactic bulge.
The LOFT burst alert system and its burst onboard trigger
Stéphane Schanne,
Diego Götz,
Hervé Le Provost,
et al.
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The ESA M3 candidate mission LOFT (Large Observatory For x-ray Timing) has been designed to study strong gravitational fields by observing compact objects, such as black-hole binaries or neutron-star systems and supermassive black-holes, based on the temporal analysis of photons collected by the primary instrument LAD (Large Area Detector), sensitive to X-rays from 2 to 50 keV, offering a very large effective area (>10 m2), but a small field of view (ø<1°). Simultaneously the second instrument WFM (Wide Field Monitor), composed of 5 coded-mask camera pairs (2-50 keV), monitors a large part of the sky, in order to detect and localize eruptive sources, to be observed with the LAD after ground-commanded satellite repointing. With its large field of view (>π sr), the WFM actually detects all types of transient sources, including Gamma-Ray Bursts (GRBs), which are of primary interest for a world-wide observers community. However, observing the quickly decaying GRB afterglows with ground-based telescopes needs the rapid knowledge of their precise localization. The task of the Loft Burst Alert System (LBAS) is therefore to detect in near-real- time GRBs (about 120 detections expected per year) and other transient sources, and to deliver their localization in less than 30 seconds to the observers, via a VHF antenna network. Real-time full resolution data download to ground being impossible, the real-time data processing is performed onboard by the LBOT (LOFT Burst On-board Trigger system). In this article we present the LBAS and its components, the LBOT and the associated ground-segment.
The LOFT ground segment
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LOFT, the Large Observatory For X-ray Timing, was one of the ESA M3 mission candidates that completed their
assessment phase at the end of 2013. LOFT is equipped with two instruments, the Large Area Detector (LAD) and the Wide Field Monitor (WFM). The LAD performs pointed observations of several targets per orbit (~90 minutes),
providing roughly ~80 GB of proprietary data per day (the proprietary period will be 12 months). The WFM
continuously monitors about 1/3 of the sky at a time and provides data for about ~100 sources a day, resulting in a total of ~20 GB of additional telemetry. The LOFT Burst alert System additionally identifies on-board bright impulsive events (e.g., Gamma-ray Bursts, GRBs) and broadcasts the corresponding position and trigger time to the ground using a dedicated system of ~15 VHF receivers. All WFM data are planned to be made public immediately. In this contribution we summarize the planned organization of the LOFT ground segment (GS), as established in the mission Yellow Book1. We describe the expected GS contributions from ESA and the LOFT consortium. A review is provided of the planned LOFT data products and the details of the data flow, archiving and distribution. Despite LOFT was not selected for launch within the M3 call, its long assessment phase ( >2 years) led to a very solid mission design and an efficient planning of its ground operations.