The Impact of Fermi on the Study of Gamma-ray Bursts
  Recent Fermi results have focused attention on gamma-ray burst's (GRB) prompt emission phase, which is rich in phenomenology and poorly understood. The broad band spectra observed by Fermi does not fit into any of the frameworks of existing theoretical models. Thus, Fermi results force new thinking of questions that were thought to be solved. I highlight here the basic open questions prior to the launch of Fermi, key Fermi results, and new theoretical ideas that emerged following these results. These include: (I) renewed interest in magnetized outflows as a way to understand the dynamics and composition; (II) interest in photospheric emission, in particular ways to broaden "Planck" spectrum to resemble the observed "Band" spectrum; (III) The puzzling origin of the high energy (LAT) photons, first observed in short GRBs; and (IV) new methods to estimate the Lorentz factor of the outflow. 
Asaf Pe'er
astro-ph.HE