Abstract. In this paper, we have made an accurate investigation of proton acceleration in GRBs and we have predicted a possible signature of cosmic rays, in a sufficiently baryon-loaded fireball, via GeV γ-ray emission produced by π 0 -meson decay. If two ungrounded assumptions are removed, namely, Bohm's scaling and a slow magnetic field decrease, the usual Fermi processes are unable to generate ultra high energy cosmic rays (UHECRs) in GRBs. We propose to develop another scenario of relativistic Fermi acceleration in the internal shock stage. We present the results of a realistic Monte-Carlo simulation of a multi-front acceleration which clearly shows the possible generation of UHECR. The amount of energy converted into UHECRs turns out to be a sizeable fraction of the magnetic energy.

The paper is devoted to the analysis of Fermi acceleration of protons in GRBs and its neutrino signature. We have compared the consequences of Bohm scaling and those of a Kolmogorov scaling, the latter being more reliable. The predictions about the energy limitation of UHE-protons by the various losses and the neutrino emissions turn out to be very sensitive to these scalings. We consider Kolmogorov scaling as the most realistic and predict a reasonable pp-neutrino emission around 100 GeV at the end of the radiative stage of the fireball expansion, for a large number of GRBs pending on their baryonic load. A second pγ-neutrino emission is expected with the acceleration of protons in the radiation free stage, but with a synchrotron loss limitation immediately followed by a severe expansion loss limitation. According to the Kolmogorov scaling, the protons could not reach the UHE-range. Anyway the large possibility of a two component neutrino emission would be an interesting clue of cosmic ray physics.

The paper is devoted to the analysis of particle acceleration in Gamma-Ray Bursts (GRBs) 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. In a recent paper we have 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. In this paper we extend 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 that the five following events naturally happen with no other parameter adaptation that the intensity of the magnetic field, that turns out to be subequipartition: i) UHECRs can be generated with a sufficient flux (≃ 1 km −2 yr −1 ) within the GZK-sphere to account for the CR-spectrum at the ankle (in the previous paper, we showed that the associated pγ-neutrino emission is tiny). 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 ≃ 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 (as predicted in

No abstract

No abstract