Hard X-ray Focal Plane Detectors onboard the FOXSI-4 sounding rocket for solar flare observation

The Focusing Optics X-ray Solar Imager (FOXSI) sounding rocket experiment enables high-resolution hard-X-ray solar observations with high sensitivity using the direct imaging method. The fourth flight, FOXSI-4, is scheduled to launch in spring 2024, aiming for the first-ever focusing imaging spectroscopic observation of a medium to large solar flare in hard X-rays. We developed wide-gap CdTe Double-sided Strip Detectors (CdTe-DSDs) for the hard X-ray focal plane detector, which achieved an energy resolution of ~1 keV (FWHM) and a high position resolution of ~ 30 µm with high detection efficiency. We also developed a new onboard data acquisition (DAQ) system with a Raspberry Pi, an FPGA board SPMU-001, and a SpaceWire interface for controlling all CdTe-DSDs and realizing fast readout of the observation data whose counting rate is estimated to be ~ 5000 counts per second. We give an overview of the hard X-ray telescope and the development of the DAQ system for the CdTe-DSDs.