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M. G. Baring (Rice University)
The principal paradigm for the generation of the non-thermal particles that are responsible for the prompt emission of gamma-ray bursts invokes diffusive shock acceleration at shocks internal to the dynamic ultrarelativistic outflow. This paper interprets burst emission spectra in the light of shock acceleration theory. Parametric fits to burst spectra obtained by the Compton Gamma-Ray Observatory (CGRO) are explored for the cases of the synchrotron and other radiation mechanisms, using a linear combination of thermal and non-thermal electron populations. These fits demand that most of the electrons that are responsible for the prompt emission reside in an intrinsically non-thermal population, strongly contrasting particle distributions obtained from acceleration simulations. They also indicate that the synchrotron self-Compton spectrum is characteristically too broad near the burst spectral peak to viably account for typical CGRO bursts. While these issues address the relationship between the thermal and non-thermal electrons, expectations for the power-law index are also discussed, using results from Monte Carlo simulations of acceleration at relativistic shocks. It is demonstrated that there is a non-universality of the power-law index, with the index depending on the shock speed, magnetic field orientation, and the type of diffusive scattering invoked. Implications for prompt emission in the EGRET band, and also GRB afterglows, are discussed.
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Bulletin of the American Astronomical Society, 36 #3
© 2004. The American Astronomical Soceity.