Development of an optical and near-infrared telescope onboard the HiZ-GUNDAM mission

The HiZ-GUNDAM (high-z Gamma-ray bursts for UNraveling the Dark Ages Mission) is a time-domain and multi-messenger astronomy mission by monitoring high-energy astronomical transient events such as gamma-ray bursts (GRBs). The HiZ-GUNDAM is designed to provide alerts of high-redshift GRBs with an ultra-wide field X-ray monitor and a co-onboard 30-cm telescope for immediate photometric follow-up observations in the visible and near-infrared. The HiZ-GUNDAM satellite automatically changes its attitude toward the discovered transient object, starts the follow-up observations with the telescope, and sends alert information including the detailed position, the apparent magnitude and photometric redshift of the transient object within one hour. This mission was selected as one of the mission concept candidates of the competitively-chosen medium-class mission of ISAS/JAXA in the mid-2020s. The basic design of the breadboard model of the telescope is undergoing, and the verification plan of it is studied. The optics are cooled down to 200 K by radiation cooling, and infrared detectors are additionally cooled down to 120 K by a mechanical cooler. All mirrors in the telescope are made of the same aluminum-alloy to reduce the alignment errors during cooling. The four-band simultaneous observation is realized by three beam splitters. The HgCdTe and HyViSi detectors are installed in this telescope. Basic technologies for these specifications are demonstrated by our other missions. In addition, the onboard detection algorithm of high-redshift GRBs by distinguishing them from nearby dusty galaxies in the orbit is also studied. In this paper, we introduce the current status of the development of the telescope onboard HiZ-GUNDAM.