Very high energy emission from gamma-ray bursts

Gamma-Ray Bursts (GRBs), the most powerful sources of gamma rays in the universe, have been detected at energies up to 95 GeV. This energy is at the verge of what is known as the Very High Energy (VHE, above 100 GeV) emission regime. VHE sources are targets for currently running and upcoming ground-based Cherenkov telescopes. It is therefore very important to understand the VHE emission mechanism(s) of GRBs. Synchrotron radiation by electrons accelerated in the external shocks of a GRB blast wave, widely accepted as the mechanism for X-ray to radio afterglow emission, has difficulty to explain and 10 GeV emission hours after the GRB trigger. We model VHE emission from interactions of cosmic-rays which are shock-accelerated in the GRB blast wave. We also compute VHE emission from electron-positron pair cascade formed in the intergalactic space by absorption of and 1 PeV gamma rays from the prompt phase of the GRB. VHE emissions from the GRBS modeled here can be tested by the ground-based air and water Cherenkov telescopes.