ASCA's Scientific PayloadsASCA carries four co-aligned, large-area X-Ray Telescopes (XRTs). At the focus of two of the telescopes is a Gas Imaging Spectrometer (GIS), while a Solid-state Imaging Spectrometer (SIS) is at the focus of the other two. All 4 instruments observe the same celestial target and obtain data simultaneously.
X-rays tend to scatter, rather than reflect cleanly, except when the incident X-rays are almost parallel to the reflecting surface (i.e., grazing). Conventional X-ray mirrors use a pair of hyperbolic and parabolic surfaces. The design of the ASCA telescopes is a conical approximation, realized as a set of closely nested concentric thin foils.
This allows for a lightweight telescope with a large effective area, which is important for spectroscopy, while sacrificing the spatial resolution somewhat.
See ASCA XRT page for more details.
The GIS is a gas imaging scintillation proportional counter and is based on the GSPC that flew on the second Japanese X-ray astronomy mission, Tenma. The GIS has a circular field of view of ~50 arcmin diameter, which is greater than that of the SIS, and a high efficiency particularly above 4 keV.
See ASCA GIS page for more details.
The SIS is the first CCD-based instrument for cosmic X-ray astronomy. Each SIS contains 4 MIT Lincoln Lab CCD chips, sensitive to X-rays in the 0.4 to 10 keV range, and provides an unprecedented spectral resolution (2% at 6 keV) over this wide energy range. All three upcoming major X-ray astronomy missions (Chandra, XMM, and ASTRO-E) will have CCD-based instruments which are improved versions of the ASCA SIS.
See ASCA SIS page for more details.
This page created by Dr. Koji Mukai (USRA) at the U.S. ASCA Guest Observer Facility.
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