High Energy Emission and Cosmic Rays from Gamma-Ray Bursts

Abstract

The paper is devoted to the analysis of particle acceleration in Gamma-Ray Bursts and its radiative consequences. Therefore we get on one hand constraints on the physics and on the other hand possible signatures of particle acceleration that could be recorded by the new gamma ray instruments. We have previously shown that UHECRs can be generated in GRBs even with conservative assumptions on the magnetic field and the scattering capability of its perturbations, provided that a suitable relativistic Fermi process is at work during the so-called "internal shock" phase. We extend here the analysis of the consequences of these assumptions to the whole prompt emission of both electrons and protons. Indeed, assuming that the magnetic field decays in $1/r^2$ and that the scattering time of particles is longer than the Bohm's assumption, in particular with a rule derived from Kolmogorov scaling, we show with no other parameter adaptation that the intensity of the subequipartition magnetic field, that: i) UHECRs can be generated with a sufficient flux within the GZK-sphere to account for the CR-spectrum at the ankle. ii) The peak energy of the gamma spectrum around 100 keV, namely the so-called $E_{peak}$, is conveniently explained. iii) A thermal component below the $E_{peak}$ is often unavoidable. iv) The cosmic rays could radiate gamma rays around 67 MeV (in the co-moving frame, which implies $\simeq 20$ GeV for the observer) due to $π^0$-decay and a low energy neutrino emission (around 0.2 GeV) associated to neutron decay and also neutrinos of energy between 5 and 150 GeV from muon decay. v) The UHECRs radiate high energy gamma rays between a few tens of MeV and 10 GeV (taking the pair creation process into account) due to their synchrotron emission with a sufficient flux to be observable.