Spectral Evolution of Two High-Energy Gamma-Ray Bursts
  The prompt emission of the gamma-ray bursts is found to be very energetic, releasing ~10^51 ergs in a flash. However, their emission mechanism remains unclear and understanding their spectra is a key to determining the emission mechanism. Many GRB spectra have been analyzed in the sub-MeV energy band, and are usually well described with a smoothly broken power-law model. We present a spectral analysis of two bright bursts (GRB910503 and GRB930506), using BATSE and EGRET spectra that cover more than four decades of energy (30 keV - 200 MeV). Our results show time evolutions of spectral parameters (low-energy & high-energy photon indices and break energy) that are difficult to reconcile with a simple shock-acceleration model. 
Y. Kaneko (1), R. D. Preece (1), M. M. Gonzalez (2 and 3), B. L.   Dingus (3), M. S. Briggs (1) ((1) UAH / NSSTC, (2) Univer...