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One of the greatest enigmas that astrophysicists currently face is the nature and the origin of the Gamma-Ray Bursts. Based on available data, it is impossible to conclude if they are local, galactic, extragalactic or a combination of all three. There is therefore a compelling need for an experiment that can measure burster distances. The Cooperative Astrophysics and Technology Satellite (CATSAT) is a small, space flight mission specificaly designed to investigate the puzzle of Gamma-Ray Bursts using an innovative multi-observation approach. This program has been accepted for phase I study in USRA's Student Explorer Demonstration Initiative (STEDI).
CATSAT uses an array of cooled silicon detectors to measure the spectra of GRBs at energies down to 500 eV for a field of view that is nearly $2\pi$ steradians. This will allow us to use the soft X-ray cutoffs, generated at energies below 2 keV by photoelectric absorption in the interstellar medium, to estimate burster distances. None of the burst experiments that have flown or are currently under construction have the ability to make such a distance measurement. While it is generally recognized that polarization measurements would place powerful constraints on models for bursters, the polarization characteristics of burster emission are also unkown. CATSAT uses the innovative technique of imaging the Earth albedo flux to study the polarization properties of the incident burst radiation. The large field of view afforded by this technique makes it the first method that is practical for measuring burst polarization. Altogether these unique observations, when placed in context by CATSAT's simultaneous measurements of conventional burst parameters, will allow tests for burst origin that will have a large impact on our understanding of these enigmatic sources.
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