An Analysis of Fermi GRB Prompt Emission Spectra with Fast and Slow-Cooling Synchrotron Models

Author: J. Michael Burgess

Abstract: We present a spectral analysis of the prompt emission of 8 bright Fermi GRBs using two physical synchrotron models (fast and slow cooling) combined with a thermal photosphere component modeled by a blackbody. The spectra are all consistent with a slow-cooling synchrotron model rather than the often predicted fast-cooling model; this presents a severe problem for the internal shock model due to the low efficiency of the slow-cooling emission mode. Analyzing the spectral evolution of both the slow-cooling synchrotron component and the thermal component provides us with clues about the temporal structure of the GRB outflow. Both components evolve separately and define distinct pulses in the energy flux lightcurves. The evolution of the spectral peak of each component follows theoretically predicted trends corresponding to synchrotron and photospheric emission.