Evaluation of the pointing accuracy of the X-Ray Imaging and Spectroscopy Mission during the first year

The X-ray Imaging and Spectroscopy Mission has two X-ray telescopes, Resolve and Xtend, both with a focal length of 5.6 m. Resolve consists of an X-ray Mirror Assembly (XMA) and a microcalorimeter array and provides a relatively narrow field of view (FoV) of a 3.05-arcminute square. Xtend consists of an XMA and an X-ray CCD camera and provides, by contrast, a large FoV of a 38.5-arcminute square. Due to Resolve's limited FoV, pointing accuracy is crucial for stable observation. We confirmed that all the measurable design requirements for pointing accuracy were met after the satellite's in-orbit boresight correction. The accuracies in determining the absolute position of the target source for both telescopes are smaller than 20 arcseconds in the conservative estimate during the commissioning phase and around 6 arcseconds at the three-sigma level, as derived from ∼1 year of observation. The shift in the aimpoint, which refers to the corresponding position on the focal-plane detector for a target point source, and its temperature dependence were also examined for each telescope. Resolve's aimpoint shift along the detector Y-axis is found to clearly depend on the base-panel temperature and is up to a few arcseconds. Nevertheless, the shift is sufficiently small that the design requirements for the accuracy in controlling the telescopes in the absolute coordinates are still well satisfied and that the potential reduction in the effective area is negligible. We confirmed that stable pointing performance was achieved by both Resolve and Xtend during the first year, without exceeding the worst-case expectations before the launch.