The end-to-end simulator of the ATHENA X-IFU Cryogenic AntiCoincidence detector (CryoAC)

The X-IFU is one of the two instrument of ATHENA, the next ESA X-ray observatory. It is a cryogenic spectrometer based on a large array of TES microcalorimeters. To reduce the particle background, the TES array works in combination with a Cryogenic AntiCoincidence detector (CryoAC). The CryoAC is a 4-pixels detector, based on ~1 cm2 silicon absorbers sensed by Ir/Au TES. It is required to have wide energy bandwidth (from 20 keV to ~1 MeV), high efficiency (< 0.014% of missed particles), low dead-time (< 1%) and good time-tagging accuracy (10 μs at 1σ). We have developed an end-to-end simulator of the CryoAC detector, composed of several modules. First, the in-flight flux of background particles is assessed by Geant4 simulations. Then, the current flow in the TES is evaluated by solving the electro-thermal equations of microcalorimeters, and the detector output signal is generated by simulating the SQUID FLL dynamics. Finally, the output is analyzed by a high-efficiency trigger algorithm, producing the simulated CryoAC telemetry. Here, we present in detail this end-to-end simulator, and how we used it to define the new baseline CryoAC configuration in the newAthena context.