High energy emission from gamma-ray bursts

Abstract

Gamma-ray bursts are the most violent stellar explosions in the universe. They are believed to be originated from deaths of massive stars (It has been confirmed that some gamma-ray bursts with durations longer than 2 s are confirmed to be associated with a special type of supernovae.) or mergers of two compact stars (e.g. mergers of double neutron stars, which have rather short time scales, and are responsible for short bursts with durations shorter than 2 s). Since the launch and commission of Fermi Gamma-Ray Space Telescope, working at 8 keV-300 GeV band, in 2008, significant achievements of gamma-ray bursts prompt emission and high-energy radiation have been made. This review will show some of the important observations of gamma-ray bursts provided by Fermi in recent years, highlighting the implications of these observations to the physics of gamma-ray bursts (including photosphere emission and magnetization of gamma-ray burst ejecta, as well as origins of GeV high-energy emission), especially the major advancements in constraining gamma-ray bursts initial velocity/Lorentz factor, constraining models of extragalactic background light, and testing Lorentz invariance violation provided by high-energy (> 100 MeV) observations made by Fermis LAT instrument.