Fermi observations of the jet photosphere in GRBs: interpretations and consequences

Author: Felix Ryde

Abstract: Fermi Gamma Ray Space Telescope observations of the prompt emission in gamma-ray bursts (GRBs) have provided evidence that several different spectral features can be present in burst spectra. One such feature is the emission from the jet photosphere, which has been shown to play a significant role in the formation of the spectrum in several strong bursts. In this talk, I will present characteristic Fermi bursts which illustrate the various appearances that the photosphere can have in GRBs. In particular, based on these observations, I will show how the dynamics of the jet can be estimated and what we can learn about the physical processes involved. I will also discuss geometrical and physical processes that will broaden the photosphere spectrum that is expected from a relativistic outflow and show how this can explain the observations. Finally, I will compare these Fermi results with the results found for the photospheric emission detected in CGRO BATSE observations.