HEAD 2003 Meeting
Session 44. Gamma-ray Bursts II
Oral, Tuesday, March 25, 2003, 6:30-7:30pm

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[44.02] Gamma Ray Burst Afterglows: Testing the Underlying Assumptions

S. A. Yost, F. A. Harrison, R. Sari (Caltech), D. A. Frail (NRAO)

Afterglow studies of gamma-ray bursts can in principle constrain fundamental parameters of the events as the evolution depends upon the explosion (its energy, geometry), its environment (density, extinction at the host) and microphysics of the relativistic shock (energy partitions, accelerated electrons' powerlaw index). We use a theoretical model to extract this information from 4 well-studied events by fitting the observations. Next we examine the similarities and differences between the events' environments and shock microphysics indicated by the best fits to this fireball model. We investigate possible deviations from the basic assumptions of the standard afterglow model, and check whether the data constrains them by requiring the model behavior to accommodate the observations. Specifically, we quantify allowed changes to the constancy of the shock's magnetic energy fraction, and to the powerlaw index of the circumburst density profile. Finally, we identify potential observations that could break the degeneracy between different acceptable models. This work was funded in part by NASA grant NAG5-5322.

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Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.