Fermi Observations of the Jet Photosphere in GRBs: Interpretations and Consequences

Fermi Gamma Ray Space Telescope observations of the prompt emission in gamma-ray bursts (GRBs) has 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 summarise the lessons learned from Fermi observations regarding the behaviour of the photosphere. In particular, I will show that the identification of the photosphere component is important in order to correctly interpret the emission. Finally, I will 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 non-thermal spectra seen in many bursts.