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A. I. MacFadyen, E. Ramirez-Ruiz (Institute for Advanced Study), W. Zhang (KIPAC/Stanford)
The recent report of long-duration (~100 s) X-ray flares following several short GRBs provides important clues for identifying the nature of their progenitor system. A possible interpretation of these observations is that the central engine stays active well beyond the burst timescale (< 3 s), continuing to emit large amounts of energy for periods of minutes or longer. This is very long compared to the dynamical and orbital timescales for a neutron star or stellar-mass black hole which are measured in milliseconds. Here we present an alternative model in which the X-ray flares are attributed to the interaction of the GRB outflow with a stellar companion at a distance of a light-minute or less. The delay from GRB to flare peak, and the flare duration are determined by the the time it takes the GRB ejecta to reach and cross the star. For main-sequence or red-giant companions, we expect these systems to be associated with evolved stellar populations or, alternatively, with star forming regions when the companion is a Helium star. The model naturally explains the association of short GRBs with both blue galaxies and with ellipticals dominated by old stellar populations.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.