We present a summary of the ground calibration of the x-ray mirror assemblies (XMAs) for the XRISM satellite, that has been performed at the x-ray beamline at NASA’s Goddard Space Flight Center. We used a scan method with a narrow x-ray pencil beam to calibrate both Resolve and Xtend XMAs, at eight different energies. In this paper, we give an overview of the measurement setup, and show the resulting on-axis and off-axis effective area response. Results of imaging performance, stray light, and performance variation across the aperture will be presented in separate publications.
The X-Ray Imaging and Spectroscopy Mission (XRISM) is an x-ray astronomy satellite being developed in collaboration between NASA, JAXA, and ESA, and is scheduled for launch in Japanese fiscal year 2022. The x-ray mirror assembly (XMA) for XRISM has been developed at NASA’s Goddard Space Flight Center (GSFC). Two units were fabricated, one each for a micro-calorimeter array (Resolve) and a CCD array (Xtend). The ground calibration and performance verification measurements for XRISM XMA were taken at the 100-m x-ray beamline at NASA/GSFC. X-ray images at the focal plane were taken by scanning across the entire mirror aperture with a 15 mm×15 mm pencil beam. These measurements were performed at seven different energies including 1.5 keV (Al Kα), 4.5 keV (Ti Kα), 6.4 keV (Fe Kα), 8.0 keV (Cu Kα), 9.4 keV (Pt Lα), 11.1 keV (Pt Lβ), 17.5 keV (Mo Kα). A method for background subtraction was developed using a back-illuminated CCD camera with a 30 mm×30 mm (i.e. 17′×17′) array at the focal plane. Results from the measurements on the imaging performance show a small energy dependence in the angular resolution. We will also present the results of the stray light measurements.
A measurement called “local spot scan (LSS)” reveals the detailed local performance of the x-ray mirror assembly (XMA) of the XRISM satellite. A 6.4 keV 10 mm×10 mm pencil beam was tiled across the mirror aperture. We extracted three local performance metrics at each spot: effective area (EA), image shift, and image profile. The EA maps on the aperture of all the quadrants (QTs) are quantitatively very similar to each other. The inner region has two times larger local EA than the outer one because of the difference in reflectivity at shallower incident angles. The pattern of the image shift is different per QT. The pattern indicates systematic shifts of reflectors by the reflector alignment structures rather than random shifts, and most area of the XMA aperture has a longer focal length than the design. The image profile was quantified using the half power diameter (HPD). There is much less variation in the HPD maps than in the image shift. The inner region has better HPD because of its better conical approximation and figure error of the reflectors. Patterns visible in the HPD maps are associated with alignment structures at a certain radial range. The local performances acquired by the LSS will be compiled into the calibration data base (CalDB) files.
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