Performance evaluation of pnCCD onboard HiZ-GUNDAM mission

We are developing a wide-field X-ray monitor onboard the HiZ-GUNDAM mission. HiZ-GUNDAM is a future satellite mission for gamma-ray burst observation to lead the time domain astronomy and multi-messenger astronomy. The pnCCD detectors will be used as a focal plane detector, which is a back-illuminated CCD and fully depleted by reverse-biased pn-junctions on front and back sides. It has a high sensitivity to low-energy X-rays and achieves a high frame rate with column-parallel readout. It was originally developed for X-ray astronomy, and its high radiation hardness has been verified on satellites such as the XMM-Newton and the eRosita mission. The detector temperature is assumed to be around −20 &deg;C, which is higher than that of usual space use CCD sensors, due to thermal design constraints. <br/> <br/> We investigated the spectral performance of pnCCDs using a small-sized device mounted on the camera system manufactured by PNDetector GmbH. Several fluorescence X-ray lines from 0.28 keV(C-K&alpha;) to 4.5keV (Ti-K&alpha;) were used for measurements. The energy resolution of 52 eV for 0.28 keV was verified, with a frame rate of 100 Hz at −20 &deg;C of operating temperature. We also made measurements of dark current for various temperatures ranging from −20 to 0 &deg;C and evaluated that the lower discriminated energy could be 123 eV even at 0 &deg;C. These results verified to satisfy the mission requirements of HiZ-GUNDAM.