Author: Peter Veres
Abstract: We present a static model which includes a generalized treatment of the acceleration phase of the GRB jet's Lorentz factor with radius. The prompt emission is produced at the photosphere by synchrotron radiation, and the GeV range radiation results from inverse Compton radiation at the deceleration radius. In this framework we are able to explain the extremely high (15 MeV) peak energy of GRB 110721A. We can also adequately fit with this model the brightest GRB's spectra observed by Fermi GBM and LAT, taking into account the response matrices of these instruments. Among other parameters, we constrained the ISM density, the fraction of energy in magnetic fields or carried by electrons.