Gamma-ray burster distances from soft X-ray observations

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Conference Proceeding

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If soft x-ray spectra can be obtained for a small set of bursts, then the burster distances can be reliably measured by the variation of absorption from the intervening neutral gas. The variation of the measured column density with burst brightness and galactic latitude provides a unique signature of the distance scale to bursts. For example, an extragalactic hypothesis would be proved if the observed column density is greatly larger than can be contributed by our own Milky Way, while a Solar System origin would be proved if the observed column density is zero. To achieve this goal, a wide field (>2 sr) detector with area greater than roughly 70 cm 2 and reasonable spectral resolution down to 0.1 keV needs to be flown for longer than roughly a year. The primary goal for this wide-field soft x-ray spectrometer would be to establish a distance scale to bursters-and this one result would by itself be the most important discovery about the biggest mystery in modern astrophysics. For other gamma-ray burst studies, the spectrometer would also measure the soft precursors and tails, search for x-ray cyclotron lines and iron lines, and be ideally suited for the discovery of Soft Gamma Repeaters. For non-burst studies, the instrument would provide longterm spectra and light curves for bright persistent sources, search for new phenomena such as the ultrasoft transients seen by Einstein, and possibly detect the shock breakout of a supernova.

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AIP Conference Proceedings

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