High-energy $γ$-ray emission from GRBs

Abstract

GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV) $γ$-ray energy band, while only a few GRBs have been observed at high photon energies ($E_γ \ut > 1$ GeV). It is also widely recognized that GRBs accelerate protons to relativistic energies and that dense media are often present nearby the sources. Within this framework we compute in detail the high-energy $γ$-ray flux from the decay of neutral pions produced through the interaction of accelerate protons with nucleons in the surrounding medium. We also take into account the local and intergalactic $γ$-ray absorption. The presence of magnetic fields around the GRB sources causes the deflection of the accelerated protons and so a temporal spread of the produced high-energy $γ$-rays with respect to the signal in the soft $γ$-ray band. Moreover, we analyze the possibility to detect the $γ$-ray signal in the GeV-TeV energy range by the ARGO detector under construction in Tibet.