Cosmic Rays and Neutrinos from Gamma Ray Bursts

Abstract

We review the hypothesis that the acceleration of protons at internal shocks in Gamma Ray Bursts (GRB) could be the origin of the ultra-high energy cosmic rays (UHECR) observed at earth, E_max > 10^19 eV. We find that, even though protons may be accelerated to such energies, their ejection into the interstellar/intergalactic medium is problematic because it is likely to be accompanied by considerable adiabatic losses in the expanding shell. The problem is circumvented by neutrons produced in photohadronic interactions, which are not magnetically bound and thus effectively ejected in the moment of their production. They can be both produced in sufficient number and be able to leave the emission region if the optical depth of the emission region to photohadronic interactions is of order 1. We show that this requirement can be fulfilled under the same conditions which allow acceleration of protons to the highest energies. The production of neutrinos in this process correlates the fluxes of cosmic rays and neutrinos, and makes the hypothesis of UHECR origin in GRBs testable.