ASTRO-H Soft X-ray Telescope (SXT)

Abstract

ASTRO-H is an astrophysics satellite dedicated for X-ray spectroscopic study non-dispersively and to carry out survey complementally, which will be borne out of US-Japanese collaborative effort. Among the onboard instruments there are four conically approximated Wolter-I X-ray mirrors, among which two of them are soft X-ray mirrors\ of which the energy range is from a few hundred eV to 15 keY, currently being fabricated in the X-ray Optics Lab at Goddard Space Flight Center. The focal point instruments will be a calorimeter (SXS) and a CCD camera (SXI), respectively. The reflectors of the mirror are made of heat-formed aluminum substrate of the thickness gauged of 152 !lm, 229 !lm, and 305 !lm of the alloy 5052 H-19, followed by epoxy replication on gold-sputtered smooth Pyrex cylindrical mandrels to acquire the X-ray reflective surface. The epoxy layer is 10 !lm nominal and surface gold layer of 0.2 !lm. Improvements on angular response over the Astro-ElISuzaku mirrors come from error reduction on the figure, the roundness, and the grazing angle/radius mismatching of the reflecting surface, and tighter specs and mechanical strength on supporting structure to reduce the reflector positioning and the assembly errors. In this paper, we report the results of calibration of the engineering model of SXT (EM), and project the quality of the flight mirrors.Keywords: X-ray Optics, X-ray Telescope, X-ray Astrophysical Instrument IntrodnctionConical approximation ofthe Wolter-I type X-ray imagers has been a major tool for spectroscopic study in the last quarter of century since the launch of a sounding rocket experiment to study SN 1987 A. The high throughput, essential for the spectroscopic study, of the telescope is provided by using thin-foil reflectors, and the continuous improvement of angular response on X-ray imaging is accomplished by switching the substrate surface smoothing scheme from earlier lacquer-dipping to recent epoxy replication that reduced the mid-frequency waviness 2 • The low micro-roughness of the surface produces specular reflection of X-rays, with high Z material such as Au, Pt, or Ir as the reflecting surface. The energy range coverage can be up to 15 ke V by lowering the grazing angle. Despite the continuous improvement over the last two decades from 4 to 1.7 arc-minutes, the demand of even better angular resolution of such thin-foil mirrors is high. The current image quality is still far from achieving the conical approximation limit, which is about 0.2 arc-minute. The difficulty comes from the relatively weak mechanical integrity of the reflectors and the imprecision in the assembly/aligmnent scheme. The improvement ofHPD from the Suzaku mirror of2 arc-minutes to the recent test of engineering model of ASTRO-H of 1 arc-minute will be the main subject of this paper.

The ASTRO-H (Hitomi) x-ray astronomy satellite

“…The X-ray mirror is very similar to the Suzaku X-ray Telescope, 20 but with a longer focal length of 5.6 m and a larger outer diameter of 45 cm. The SXT [21][22][23][24][25] consists of three parts: an X-ray mirror, a stray light baffle called the pre-Collimator, and a thermal shield to keep the mirror temperature at around 20 • C. The mirror is a conically approximated Wolter I grazing incidence optic with 203 nested shells. Each shell is segmented into four quadrants.…”

Astro-H/Hitomi data analysis, processing, and archive

“…Hitomi was equipped with four different instruments that together cover a wide energy range of 0.3 to 600 keV. The soft x-ray spectrometer (SXS 2 ), which pairs a lightweight soft x-ray telescope 3 (SXT) with an x-ray calorimeter spectrometer, provides nondispersive spectroscopy with <7 eV resolution in the 0.3 to 12 keV energy range with a field-of-view (FoV) of about 3 arc min. Three additional scientific instruments extend the energy bandpass of the observatory.…”

“…Three additional scientific instruments extend the energy bandpass of the observatory. The soft x-ray imager (SXI 4 ) expands the FoV with a new generation CCD camera in the energy range of 0.5 to 12 keV at the focus of the second lightweight SXT 3 ; the hard x-ray imager (HXI, 5,6 two units) performs sensitive imaging spectroscopy in the 5-to 80-keV band; and the nonimaging soft gamma-ray detector (SGD, 7 two units) extends Hitomi's energy band to 600 keV. In addition, there are three subsystems: two for the SXS, the modulated x-ray source (MXS 8 to calibrate the gain) and the anticoincidence system; and one for the HXI, the Canadian Astro-H Metrology System (CAMS 9 ) that tracks the movement of the extended optical bench (EOB).…”

Cryogen-free operation of the Soft X-ray Spectrometer instrument

“…By mid-March 2016, the required SXS commissioning activities were complete except for the final task of opening the dewar gate valve to give the SXS detectors an unobstructed view of the sky through their x-ray optics. 13 On March 26, 2016, the Hitomi satellite suffered a catastrophic loss of attitude control, loss of communication, and spacecraft breakup. 2,5 At the time, the cause of the communications loss was not known, and an eventual recovery still seemed plausible.…”