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U. D. Desai, L. E. Orwig (NASA/GSFC), L. N. Mertz (Digiphase Technology), C. C. Gaither III (CNA Corp.), W. M. Gibson (Center for X-Ray Optics, U. of Albany)
The study of transient astrophysical phenomena (e.g. solar flares, x-ray bursters, and gamma ray bursts) needs the development of new instruments capable of simultaneously making measurements with high spatial, temporal, and spectral resolution. Detectors for high spectral and temporal measurments do exist. However, for imaging at high energies only a few options are available. Shadow casting techniques have been employed to image hard x-rays. These techniques employ total absorption of x-rays and gamma rays to indirectly achieve imaging. We describe a design for an x-ray telescope based on a two shadow masks which resemble Fresnel Zone Plates (FZP) (although they do not involve any diffraction) which give simple straight bands for well separated point sources. Such plates are in principle suitable for use on small satellites. Most single plane coded aperture imaging requires very high spatial resolution detectors to achieve high angular resolution. In our scheme the image plane detector can have coarse resolution, but still provide high angular resolution since it has only to resolve the Moire-fringes rather than the finest features of the zone plate.
The telescope that we have developed uses zone plates made from 1mm-thick tungsten with a finest feature of 41 microns. We present very preliminary results of exposure of such a telescope to a nearly parallel x-ray beam.
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