The X-Ray Telescope on board ASCA

Abstract The ASCA instrument uses identical conical foil X-ray mirrors for its four telescopes. One of the major advantages of ASCA’s telescopes is the first time ever use of X-ray imaging over a broad energy band and high throughput for conducting astronomical spectroscopy. Nested thin foil reflectors make possible a large effective area up to 10 keV, even under the tight weight restriction of the ASCA spacecraft. The expected characteristics of the ASCA mirrors are summarized based on ray tracings and pre-flight calibrations. The total effective area of four telescopes at 1 and 7 keV are ~ 1200 and 600 cm2, respectively. The image size (half power diameter : HPD) is about 3ʹ. The field of view is 24ʹ and 16ʹ FWHM for 1 and 7 keV, respectively. Observations of several X-ray sources from space during the performance verification phase have confirmed those performances as well as the alignment of the optical systems.