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N.M. Lloyd, V. Petrosian (Stanford University)
We present the wide variety of spectral evolution present in a sample of about 80 GRBs, and attempt to categorize these bursts (both by eye, and using new methods involving the cross-correlation function between the time histories of the spectral parameters) according to their evolutionary behavior. We discuss in particular the correlations observed between the various spectral parameters; we show that a majority of the correlations are primarily due to instrumental effects, but that the physical processes involved also play a significant role. We present a physical explanation for the temporal evolution of the spectral parameters, in terms of synchrotron emission from internal shocks. In particular we show that allowing for a ``smooth cutoff'' to the electron energy distribution, an anisotropic distribution for the electron pitch angles, and - in a few cases - synchrotron self-absorption, synchrotron emission can explain the time resolved behavior of the spectral parameters throughout a burst, if we regard each pulse a separate/independent emission episode. Finally, we briefly discuss how the presence of other emission mechanisms may affect our model of emission from GRBs.
The author(s) of this abstract have provided an email address for comments about the abstract: nicole@urania.stanford.edu