18 July 2016 Point spread function of ASTRO-H Soft X-ray Telescope (SXT)
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ASTRO-H (Hitomi) satellite equips two Soft X-ray Telescopes (SXTs), one of which (SXT-S) is coupled to Soft X-ray Spectrometer (SXS) while the other (SXT-I) is coupled to Soft X-ray Imager (SXI). Although SXTs are lightweight of ~42 kgmodule-1 and have large on-axis effective area (EA) of ~450 cm2 at 4.5 keV module-1 by themselves, their angular resolutions are moderate ~1.2 arcmin in half power diameter. The amount of contamination into the SXS FOV (3.05 x 3.05 arcmin2) from nearby sources was measured in the ground-based calibration at the beamline in Institute of Space and Astronautical Science. The contamination at 4.5 keV were measured with sources distant from the SXS center by one width of the FOV in perpendicular and diagonal directions, that is, 3 and 4.5 arcmin-off, respectively. The average EA of the contamination in the four directions with the 3 and 4.5 arcmin-off were measured to be 2 and 0.6% of the on-axis EA of 412 cm2 for the SXS FOV, respectively. The contamination from a source distant by two FOV widths in a diagonal direction, that is, 8.6 arcmin-off was measured to be 0.1% of the on-axis at 4.5 keV. The contamination amounts were also measured at 1.5 keV and 8.0 keV which indicated that the ratio of the contamination EA to that of on-axis hardly depended on the source energy. The off-axis SXT-I images from -4.5 to 27 arcmin were acquired at intervals of 4.5 arcmin for the SXI FOV of 38 x 38 arcmin2. The image shrinked as the off-axis angle increased. Above 13.5 arcmin of off-angle, a stray appeared around the image center in the off-axis direction. As for the on-axis image, a ring-shaped stray appeared at the edge of SXI of ~18 arcmin distant from the image center.
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Takayuki Hayashi, Toshiki Sato, Naomichi Kikuchi, Ryo Iizuka, Yoshitomo Maeda, Manabu Ishida, Sho Kurashima, Nozomi Nakaniwa, Takashi Okajima, Hideyuki Mori, Yang Soong, Peter J. Serlemitsos, "Point spread function of ASTRO-H Soft X-ray Telescope (SXT)", Proc. SPIE 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray, 99055D (18 July 2016); doi: 10.1117/12.2232007; https://doi.org/10.1117/12.2232007

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