Soft X-Ray Imager (Sxi) For Xtend Onboard X-Ray Imaging And Spectroscopy Mission (Xrism)

Soft X-ray Imager (SXI) is the X-ray CCD camera onboard X-Ray Imaging and Spectroscopy Mission (XRISM) that is scheduled to be launched in Japanese fiscal year 2022. Combining the SXI with an X-ray mirror assembly, we realize the Soft X-ray Imaging Telescope (Xtend) with a focal length of 5.6 m and a field of view of 38 arcmin square. The high quantum efficiency of the focal-plane sensor, P-channel back-illumination type CCD, brings about the wide effective energy range from 0.4 to 13 keV with moderate energy resolution. Although the design of the SXI for XRISM is basically identical to that for Hitomi satellite, we have applied several improvements to the CCDs in terms of the charge transfer inefficiency (CTI) and the optical blocking performance. For the former issue, we introduce a notch implant in the charge transfer path to reduce the CTI increase in orbit. For the latter, we change the design of aluminum layers on the incident surface of the CCDs to decrease incoming visible light and/or infrared. Four flight model (FM) CCDs have been selected considering several items including energy resolution at 5.9 keV, CTI, dark current, etc. We have also completed calibration campaign for all the FM CCDs. Initial analyses show that the response function for monochromatic X-rays is basically the same as that of Hitomi CCDs. Front-end ASIC have been confirmed to properly function even after the long-term storage after the manufacture for Hitomi SXI. Then the analog electronics for driving CCDs and for processing the output analog signals have been implemented. Their functional tests have been completed with no problem. The focal plane including the single-stage Stirling cooler has been assembled. Production of key parts in SXI sensor body such as contamination blocking filter and onboard calibration source has been finished and they are waiting for assemble. The digitized signals of the CCD are corrected step by step before conversion to X-ray energy. We are preparing calibration database for the correction such as CTI, gain, and line redistribution function.