UHECR acceleration at GRB internal shocks
Résumé
To investigate whether gamma-ray bursts could be the sources of ultra-high energy cosmic-rays (UHECRs), we developed a Monte Carlo code to compute the acceleration of particles at mildly relativistic shocks. This code includes energy losses and handles particle escape according to specific prescriptions. We showed that particle acceleration can indeed be efficient, including for heavy nuclei, which survive photo-dissociation for a large range of gamma-ray bursts luminosities. However, only the models assuming that the prompt emission represent only a very small fraction of the energy dissipated at internal shocks, and that most of this dissipated energy is communicated to accelerated cosmic-rays, are able to reproduce the magnitude of the diffuse UHECR flux expected on Earth. For these models, we showed that the shape of the UHECR spectrum can be well reproduced above the ankle and the evolution of the composition is compatible with the trend suggested by Auger data.