Soft X-ray Imager of the Xtend system on board XRISM
Hirofumi Noda, Koji Mori, Hiroshi Tomida, Hiroshi Nakajima, Takaaki Tanaka, Hiroshi Murakami, Hiroyuki Uchida, Hiromasa Suzuki, Shōgo Kobayashi, T. Yoneyama, Kouichi Hagino, Kumiko Nobukawa, Hideki Uchiyama, Masayoshi Nobukawa, Hironori Matsumoto, Takeshi Go Tsuru, M. Yamauchi, Isamu Hatsukade, Hirokazu Odaka, Takayoshi Kohmura, K. Yamaoka, Tessei Yoshida, Yoshiaki Kanemaru, Junko S. Hiraga, Tadayasu Dotani, Masanori Ozaki, H. Tsunemi, Jin Sato, Toshiyuki Takaki, Yuta Terada, Keitaro Miyazaki, Kohei Kusunoki, Yoshinori Otsuka, Haruhiko Yokosu, Wakana Yonemaru, Kazuhiro Ichikawa, Hanako Nakano, Reo Takemoto, Tsukasa Matsushima, Reika Urase, Jun Kurashima, Kotomi Fuchi, Kaito Hayakawa, Masahiro Fukuda, Takamitsu Kamei, Yoh Asahina, Shun Inoue, Yuki Amano, Yuma Aoki, Yamato Ito, Tomoya Kamatani, Kouta Takayama, T. Sako, Marina Yoshimoto, Kohei Shima, Mayu Higuchi, Kaito Ninoyu, Daiki Aoki, Shun Tsunomachi, Kiyoshi Hayashida
Abstract
Abstract The Soft X-ray Imager (SXI) is the X-ray charge-coupled device (CCD) camera for the soft X-ray imaging telescope Xtend installed on the X-ray Imaging and Spectroscopy Mission (XRISM), which was adopted as a recovery mission for the Hitomi X-ray satellite and was successfully launched on 2023 September 7 (JST). In order to maximize the science output of XRISM, we set the requirements for Xtend and found that the CCD set employed in the Hitomi/SXI or similar, i.e., a $2 \times 2$ array of back-illuminated CCDs with a $200\, \mu$m-thick depletion layer, would be practically best among the available choices, when used in combination with the X-ray mirror assembly. We designed the XRISM/SXI, based on the Hitomi/SXI, to have a wide field of view of $38^{\prime } \times 38^{\prime }$ in the 0.4–13 keV energy range. We incorporated several significant improvements from the Hitomi/SXI into the CCD chip design to enhance the optical-light blocking capability and to increase the cosmic-ray tolerance, reducing the degradation of charge-transfer efficiency in orbit. By the time of the launch of XRISM, the imaging and spectroscopic capabilities of the SXI had been extensively studied in on-ground experiments with the full flight-model configuration or equivalent setups and confirmed to meet the requirements. The optical blocking capability, the cooling and temperature control performance, and the transmissivity and quantum efficiency to incident X-rays of the CCDs were also all confirmed to meet the requirements. Thus, we successfully completed the pre-flight development of the SXI for XRISM.