AAS Meeting #193 - Austin, Texas, January 1999
Session 87. Gamma-Ray Bursts II
Oral, Friday, January 8, 1999, 2:00-3:30pm, Ballroom A

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[87.03] The Spectral Evolution of Gamma-Ray Bursts

A. Crider, E. P. Liang (Rice University), R. D. Preece, M. S. Briggs, G. N. Pendleton, W. S. Paciesas (U. Alabama in Huntsville), D. L. Band, J. L. Matteson (UC San Diego)

The discovery of a gamma-ray burst (GRB) optical counterpart with a measurable redshift seems to have shown that the sources are cosmological in origin. The observed fading multi-wavelength afterglows are so far consistent with the simple relativistic blastwave model which radiates via a synchrotron shock. However, the emission mechanism resulting in the prompt gamma rays remains a mystery. We report on our discovery and interpretation of two important characterstics in the spectral evolution of GRBs which can be used to test possible emission mechanisms. We have found that the peak of the \nu F\nu decays linearly with energy fluence (=\intt'=0t'=t \rm{F\nu}(t') dt'). We have also found that the asymptotic spectral slope below the peak in \nu F\nu can be as steep or steeper than a blackbody, possibly ruling out models such as the synchrotron shock model. We propose that these two results suggest saturated Comptonization as the dominant emission mechanism during the early phase of GRBs.

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The author(s) of this abstract have provided an email address for comments about the abstract: acrider@spacsun.rice.edu

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