T-08

Through Thick and Thin: Spectral Evolution of GRBs and Afterglows

Edison Liang, Anthony Crider, Markus Boettcher and Ian Smith (Rice University)

We summarize the spectral evolution signatures of GRBs and their afterglows based on comprehensive analyses of data from BATSE, BeppoSAX and other space-based and ground-based experiments whenever available. We confront spectral models based on relativistically expanding shells which emit via synchrotron, bremsstrahlung and inverse Compton, for both Thomson thick and thin limits, with the spectral evolution data. We will discuss the difficulties with various models and constraints on the energetics, Lorentz and beaming factor, lepton content and other physical parameters of the explosion. In particular the transition time from the GRB to afterglow, and the power-law decay index and spectral slope of the afterflow may provide important diagnostics.