"Thermal emission from gamma-ray bursts" Dr. Asaf Pe'er
CFA/ITC I will discuss recent evidence for a thermal emission component that accompanies the non-thermal emission during the prompt phase of GRBs. I argue that this component is naturally explained by considering emission from the photosphere, taking into account high latitude emission from optically thick relativistically expanding plasma. The thermal flux is expected to decay at late times as F_BB ~ t^{-2}, and the observed temperature as T ~ t^{-\alpha}, with \alpha ~ 1/2 - 2/3. I will discuss some of the latest theoretical progress, including the theory of multicolor black body emission from relativistically expanding plasma. These theoretical predictions are in very good agreement with the observations. Finally, I will discuss three implications of this interpretation: (a) The relation between thermal emission and high energy, non-thermal spectra observed by FERMI, with particular emphasis on the peculiar GRB090902B. (b) The use of thermal emission to directly measure the Lorentz factor of the flow and the initial radius of the jet. (c) I argue that lack of detection of thermal component can be used to constrain the composition of GRB jets.