ASCA's X-ray Telescopes
The four X-ray telescopes (XRT) onboard ASCA were built by NASA's Goddard Space Flight Center and Nagoya University. The basic design of the telescope approximates the conventional opticals-paired hyperbolic and parabolic surfaces-with conical surfaces realised as a set of closely nested concentric thin foils (120 per telescope) held together in quadrants by metal fittings. The foils are made of aluminum and coated with 10 to 20 microns of acryllic and 60 nm of gold, which provided the reflecting surface.
Although the use of foils, which cannot be smoothed by polishing, reduces the sharpness of the image compared with conventional X-ray optics, it does provide a larger collecting area and broader pass band.
The "vital statistics" of the four XRT combined are as follows:
- Effective Area: 1,300 cm**2 at 1 keV; 600 cm**2 at 7 keV
- Pass band: up to 12 keV
- Field of View (FWHM): 24 arcmin at 1 keV, 16 arcmin at 7 keV
- Angular Resolution: 2.9 arcmin HPD (Half Power Diameter)
References: Serlemitosos, P. J. et al. 1995, "The X-ray Telescope with ASCA", Publ. Astron. Soc. Japan, 47, 105 Tsusaka, Y. et al. 1995, "Characterization of the Advanced Satellite for Cosmology and Astrophysics x-ray telescope: preflight calibration and ray tracing", Applied Optics, 34, 22 Tsusaka, Y. et al. 1994 "Calibration of Astro-D telescope with an x-ray pencil beam", SPIE, 2011, 517 Kunieda, H. et al. 1993, Jpn, J. Appl. Phys. 32, 4805
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