Author: Frédéric Daigne
Abstract: Recent Fermi/GBM observations suggest that, at least in some bursts, the soft gamma-ray prompt emission is made of two components with distinct spectral evolutions. We will show that these results favor the scenario where the prompt GRB emission is dominated by non-thermal dissipation above the photosphere, with a sub-dominant photospheric contribution. We will discuss how the observed spectral evolution can be reproduced in this scenario. Finally, we will summarize the constraints that we obtain on the composition and acceleration mechanism of GRB outflows, and on the physical conditions in the region where the non-thermal emission is produced.