Fermi observations of GRBs | Eleonora Troja ( NASA Goddard Space Flight Center University of Maryland – College Park )

High-energy observations of gamma-ray bursts (GRBs) with the Fermi satellite have enabled detailed studies of the temporal and spectral behaviour over seven decades in energy (from 8 keV to ~100 GeV) and provided new insight into the emission mechanisms of these powerful outbursts. I will briefly outline some highlights from Fermi GRBs observations, along with their possible implications. Key observational results include: 1) the detection of an additional spectral component at GeV energies; 2) the late onset and longer duration of the high-energy (>100 MeV) emission, compared to the low-energy (<1 MeV) prompt emission; 3) stringent limits on the variation of the speed of light with photon energy; 4) evidence for a subset of extremely relativistic and energetic stellar explosions, challenging some of the most popular GRB models.