Hard X-Ray Telescope (HXT)
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ASTRO-H Hard X-ray Telescope (HXT) Hisamitsu Awakia, Hideyo Kuniedab, Akihiro Furuzawab, Yoshito Habab, Takayuki Hayashic, Ryo Iizukad, Kazunori Ishibashib, Manabu Ishidac, Masayuki Itohe, Tatsuro Kosakaf, Yoshitomo Maedac, Hironori Matsumotob, Takuya Miyazawab, Hideyuki Moric, Hosei Naganob, Yoshiharu Nambag, Yasushi Ogasakah, Keiji Ogia, Takashi Okajimai, Satoshi Sugitaa, j b b j h Yoshio Suzuki , Keisuke Tamura , Yuzuru Tawara , Kentato Uesugi , Koujun Yamashita and Shigeo Yamauchik aEhime University, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan; bNagoya University, Furo-cho, Chikusa, Nagoya 464-8602, Japan; cISAS/JAXA, Yoshinodai, Chuou, Sagamihara 229-8510, Japan; dChuo University, Kasuga, Bunkyo, Tokyo 112-8551, Japan; eKobe University, Tsurukabuto, Nada, Kobe 657-8501, Japan; fKochi University of Technology, Tosayamada-cho, Kami, Kochi 782-8502, Japan; gChubu University, Matsumoto-cho, Kasugai, Aichi 487-8501, Japan; hJapan Science and Technology Agency, 5-1 Gobancho, Chiyoda, Tokyo 102-0076, Japan; iNASA’s Goddard Space Flight Center, Greenbelt, MD 20771, USA; jJASRI/SPring-8, Sayo-cho, Sayo, Hyogo 679-5198, Japan; kNara Women’s University, Kitauoyanishi-machi, Nara, Nara 630-8506, Japan ABSTRACT The new Japanese X-ray Astronomy satellite, ASTRO-H will carry two identical hard X-ray telescopes (HXTs), which cover 5 to 80 keV, in order to provide new insights into frontier of X-ray astronomy. The HXT mirror surfaces are coated with Pt/C depth-graded multilayers to enhance hard X-ray effective area by means of Bragg reflection, and 213 mirror reflectors with a thickness of 0.22 mm are tightly nested confocally in a telescope. The production of FM HXT-1 and HXT-2 were completed in 2012 and 2013, respectively. The X-ray performance of HXTs were measured at the synchrotron radiation facility SPring-8/ BL20B2 Japan. The total effective area of two HXTs is about 350 cm2 at 30 keV and the angular resolution of HXT is about 1.’9 in half power diameter at 30 keV. The HXTs are in the clean room at ISAS for waiting the final integration test. Keywords: Hard X-rays, hard X-ray telescope, multilayer, depth-graded multilayer, ASTRO-H, HXT 1. INTRODUCTION The new Japanese X-ray Astronomy satellite, ASTRO-H will be launched on HII-A, the Japan’s primary large vehicle in 2015 [1]. ASTRO-H will carry four X-ray telescopes (XRTs), two soft X-ray imaging Telescopes (SXT) and two Hard X-ray imaging Telescopes (HXT) for the wide-band spectroscopy between 0.3 and 80 keV (see Figure 1). The hard X- ray imaging system is configured with Hard X-ray Imagers (HXI) which are the focal plane detectors of HXTs placed on the HXI plate of the extensible optical bench (EOB). The focal length of 12 m will be realized by extending the EOB. The first full hard X-ray telescope was launched as a US-Japan international balloon experiment – InFOCμS – in 2001. In its maiden and two later flights, several X-ray sources (including Cyg X-1) were imaged in 20-40 keV to demonstrate its performance [2][3]. The hard X-ray reflectors onboard InFOCμS employed tightly-nested, conically-approximated thin-foil Wolter-I optics, and their reflector surfaces were coated with Pt/C depth-graded multilayers to enhance hard X- ray effective area by means of Bragg reflection [4]. The following balloon experiment SUMIT was performed in 2006 on the initiative of Nagoya University [5]. The success of the InFOCμS and SUMIT missions has been inherited by the ASTRO-H mission by JAXA. *[email protected] Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, edited by Tadayuki Takahashi, Jan-Willem A. den Herder, Mark Bautz, Proc. of SPIE Vol. 9144, 914426 · © 2014 SPIE CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2054633 Proc. of SPIE Vol. 9144 914426-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/28/2014 Terms of Use: http://spiedl.org/terms ASTRO-H HXTs are designed to have total effective area of greater than 300 cm2 at 30 keV and an angular resolution of 1.’7 (half power diameter), so that the hard X-ray imaging system of ASTRO-H will have a detection sensitivity 100 times higher than that of Suzaku [1] (Figure 2). ASTRO-H hard X-ray imaging system will provide new insights into frontier of X-ray astronomy. In the next sections, design parameters of HXT are summarized together with those of the pre-collimators and thermal shields. In the third section, production of HXTs is shown, and the ground calibration is described in the section four. Soft X-ray Telescope 10 -4 (Au coating) 1 mCrab'', Continuumsensitivity' (for pointsources) AE /E=0,5, 100 ks 10 -5 MP .10 iu,CrabSuzakuHXD (PIN) STT Suzakr-HXD (Gî0) 10-6 x100 10 -7 J AST h0 GÓ ASTRO-H HX/HXT Exien e 10-8 5 10 20 50 100 200 500 Figure 1 Configuration on the space craft Figure 2 Sensitivity in the hard X-ray region, assuming the energy resolution ΔE/E=0.5 and the exposure time of 100 ks. 2. HARD X-RAY TELESCOPE The HXT was designed based on the InFOCµS and SUMIT balloon-borne experiment [5][6] under the constraint on the space within the nose fairing of the HII-A rocket. Figure 3 shows a schematic view of the current design of HXT, and the design parameters of HXT are listed in Table 1. The basic design parameters of the HXT are 12 m focal length, 450 mm diameter, and 200 mm long foils. HXT consists of three components: two thermal shields (TS) [7], a pre-collimator (PC) [8], and reflector mirrors (primary and secondary mirrors). HXT has a reference cube, which is used to find the optical axis of a telescope with an accuracy of 5”. TS is used to cover the entrance side and bottom side of the telescope in order to reduce the radiative coupling between the HXT mirrors and the space/inside of the satellite [7][9]. TS is made of a polyethylene teleftalate (PET) film as thin as 2.5 μm, coated with an aluminum layer with a thickness of 30 nm, which has low solar absorptance and low infrared emissivity. Since the energy band of HXI covers 5 keV at the lower end, total thickness of PET equivalent thin film is determined to be 5 μm, in which the X-ray transmission of 5 μm PET is 98 %. In order to give enough mechanical strength to survive in various environments, a stainless steel mesh with a wire pitch, width, and thickness of 3 mm, 0.1 mm and 0.25 mm, respectively, is used to support the thin film. The transmission of soft X-rays down to 8 keV is 93 %. PC (or stary-light baffle) consists of thin cylindrical shells, which are called blades. The Suzaku’s PCs were mechanically independent from the mirror housing [10], but in the ASTRO-H HXT, the PC is integrated into the mirror housing, so that stray light is efficiently reduced without any loss of the on-axis effective area [11]. The height of the Proc. of SPIE Vol. 9144 914426-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/28/2014 Terms of Use: http://spiedl.org/terms blade measured from the top edge of the primary foil is determined to be 50 mm, in order to eliminate the secondary reflection from > 20’ off-axis from the HXI FOV (32 mm ×32 mm). Since the blade is installed in the top alignment bars (see Figure 3), there is a gap of 15 mm between the top edge of the mirror foil and the bottom edge of the blade. Thus the length of the blade is determined to be 35 mm. Table 1 Design parameters of the HXT Component Item HXT Thickness of aluminum coat 30 nm m480 m480 Thermal Reference Reference cube shield shield Thermal Thermal Film thickness 5 μm (PET) shield 1111111 1111111 NIIIIIIIIIIIII NIIIIIIIIIIIII II II I I I -collimator -collimator Pre Pre support SUS mesh + Al frame IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII + GFRP spacer Pre- Blade height 50 mm mirror mirror Primary Primary - - collimator Blade material Aluminum, t0.15 mm Focal length 12 m tab tab Mount Mount t0.22 mm reflector H200 mm mirror mirror Secondary Secondary 3 segmented Mirror Number of nest 213 shield shield Thermal Number of 1278 reflector/telescope Figure 3 Schematic view of the HXT Reflector surface Pt/C multilayer The blade thickness is 150 μm, which is thinner than that of the mirror substrate, and aluminum was selected as the blade material, because we had an experience of producing the PC blades made of aluminum for the Suzaku XRTs. Although a 150 μm thickness aluminum is transparent for photons above 50 keV, we confirmed that it does not affect the sensitivity of hard X-ray imaging system, since the X-ray background is very weak above 50 keV [8]. The HXT mirror employs conically-approximated thin-foil Wolter-I 1000 optics [6]. The approximated parabolic and hyperbolic foils are called primary and secondary reflectors in Figure 3, respectively. Image blurring due to the conical approximation is estimated to be about 0.’3 which is smaller than the requirement for the HXT. These 100 reflectors are held at their desired location and confocally aligned by the grooves of alignment bars on each top and bottom edge of the reflectors. The diameters of the innermost and the outermost reflectors are 120 mm and 450 mm, respectively. To achieve high aperture efficiency despite the small incident angle, we use 10 I , I , I . 20 40 60 80 aluminum substrate with a thickness of 0.2 mm and a length of 200 o Energy [keV] mm.