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 °C, which is higher than that of usual space use CCD sensors, due to thermal design constraints.
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-Kα) to 4.5keV (Ti-Kα) 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 °C of operating temperature. We also made measurements of dark current for various temperatures ranging from −20 to 0 °C and evaluated that the lower discriminated energy could be 123 eV even at 0 °C. These results verified to satisfy the mission requirements of HiZ-GUNDAM.
HiZ-GUNDAM is a future satellite mission whose mission concept was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s competitive medium-class mission. HiZ-GUNDAM will lead time-domain astronomy in 2030s, and its key sciences are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. Two mission payloads are aboard HiZ-GUNDAM to realize these two scientific issues. The wide field X-ray monitors which consist of Lobster Eye optics array and focal imaging sensor, monitor ~0.5 steradian field of view in 0.5–4 keV energy range. The near infrared telescope with an aperture size of 30 cm in diameter performs simultaneous 5-band photometric observation in 0.5–2.5 μm wavelength with Koester’s prism for X-ray transients discovered by Wide Field X-ray Monitor. In this paper, we introduce the mission overview of HiZ-GUNDAM while the information contained herein may change in future studies.
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