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What Spectroscopy is Telling Us About Gamma-Ray Bursts by Rob Preece 10 August 2001 The current scenario for gamma-ray bursts (GRBs) involves colliding relativistic winds for the prompt GRB emission phase and a single decelerating blastwave for the afterglow phase. The afterglows are modeled quite well by synchrotron emission from relativistic shock-accelerated electrons. GRB spectra have been observed by BATSE to have a low-energy power-law spectral index greater than -2/3 (for positive photon number indices) indicate a problem with the currently-accepted optically-thin synchrotron emission model. Spectra that do not violate this condition can also test predictions from the synchrotron shock model, since synchrotron emission from a power-law distribution of electrons is responsible for both the low-energy and high-energy power-law portions of the resulting spectra. We find that the inferred relationship between the two spectral indices of observed GRB spectra is inconsistent with the constraints from the simple optically-thin synchrotron shock emission model. I will discuss these issues in the context of current ideas about burst progenitors and production mechanisms.
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