XRISM (X-Ray Imaging and Spectroscopy Mission) is an astronomical satellite with the capability of highresolution spectroscopy with the X-ray microcalorimeter, Resolve, and wide field-of-view imaging with the CCD camera, Xtend. The Xtend consists of the mirror assembly (XMA: X-ray Mirror Assembly) and detector (SXI: Soft X-ray Imager). The components of SXI include CCDs, analog and digital electronics, and a mechanical cooler. After the successful launch on September 6th, 2023 (UT) and subsequent critical operations, the mission instruments were turned on and set up. The CCDs have been kept at the designed operating temperature of −110°C after the electronics and cooling system were successfully set up. During the initial operation phase, which continued for more than a month after the critical operations, we verified the observation procedure, stability of the cooling system, all the observation options with different imaging areas and/or timing resolutions, and operations for protection against South Atlantic Anomaly. We optimized the operation procedure and observation parameters including the cooler settings, imaging areas for the specific modes with higher timing resolutions, and event selection algorithm. We summarize our policy and procedure of the initial operations for SXI. We also report on a couple of issues we faced during the initial operations and lessons learned from them.
XRISM (X-ray Imaging and Spectroscopy Mission) is an X-ray astronomy satellite developed in collaboration with JAXA, NASA and ESA. It successfully launched on Sept. 7, 2023. Two complementary X-ray telescopes, Resolve and Xtend are on-board XRISM. Resolve uses the pixelized X-ray micro calorimeter developed by NASA/GSFC and has very high energy resolution of 5 eV. On the other hand, Xtend uses an X-ray CCD camera as its focal plane detector which has high spatial resolution and a wide field of view. We evaluated the performance of the X-ray Mirror Assembly (XMA) for Xtend using data observed during the commissioning and PV phases of XRISM. To verify the imaging performance, the Point Spread Functions (PSF) generated from the observations of NGC 4151 and PDS 456 were compared with the ground-calibration results. The results show that the imaging performance of Xtend-XMA is not significantly different from that of the ground calibration, and that it meet the requirement. The effective area was verified by comparing the results of simultaneous observations of 3C 273 by XRISM and four X-ray astronomy satellites (Chandra, XMM-Newton, NuSTAR, and Swift). The results of the fitting of the X-ray spectrum of Xtend show no significant difference from the results of other satellites, suggesting the effective area used for fitting is correct. The on-axis position on the detector was estimated from the intensity of the Abell 2029 observations at four off-axis angles. The on-axis is about 40 arcsec away from the aim point, and the decrease in effective area at the aim point is less than 1%. Stray light observations of the Crab Nebula at 60 arcmin off-axis were obtained at two different satellite roll angles. The stray light intensity obtained at each roll angle was significantly different, verifying the dependence of the stray light on the roll angle.
Xtend is one of the two telescopes onboard the X-ray imaging and spectroscopy mission (XRISM), which was launched on September 7th, 2023. Xtend comprises the Soft X-ray Imager (SXI), an X-ray CCD camera, and the X-ray Mirror Assembly (XMA), a thin-foil-nested conically approximated Wolter-I optics. A large field of view of 38′ × 38′ over the energy range from 0.4 to 13 keV is realized by the combination of the SXI and XMA with a focal length of 5.6 m. The SXI employs four P-channel, back-illuminated type CCDs with a thick depletion layer of 200 μm. The four CCD chips are arranged in a 2×2 grid and cooled down to −110°C with a single-stage Stirling cooler. Before the launch of XRISM, we conducted a month-long spacecraft thermal vacuum test. The performance verification of the SXI was successfully carried out in a course of multiple thermal cycles of the spacecraft. About a month after the launch of XRISM, the SXI was carefully activated and the soundness of its functionality was checked by a step-by-step process. Commissioning observations followed the initial operation. We here present pre- and post-launch results verifying the Xtend performance. All the in-orbit performances are consistent with those measured on ground and satisfy the mission requirement. Extensive calibration studies are ongoing.
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