Which acceleration process for ultra high energy cosmic rays in gamma ray bursts?

Abstract

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.

Hadronic Models for the Extra Spectral Component in the Short GRB 090510

“…The very high bulk Lorentz factor and high magnetic field strengths in outflows of gamma-ray burst (GRB) make GRBs potential sources of ultra-high-energy cosmic rays (UHECRs ;Waxman 1995;Vietri 1995;Gialis & Pelletier 2004). Recent time-resolved detections of GeV photons with Fermi/LAT from GRB 080916C and GRB 090510 (Abdo et al 2009a,b) reveal that the minimum Lorentz factor Γ min , required to make the sources optically thin for such GeV photons, should be 1000.…”

Astroparticle yield and transport from extragalactic jet terminal shocks

“…Few astrophysical sources seem to be suited for accelerating relativistic particles up to such energies. We can cite gamma-ray bursts (Waxman (1995), Gialis & Pelletier (2004) and references therein), shock waves in large scale structures (Norman et al, 1995) and active galactic nuclei. The terminal shocks of Fanaroff-Riley type II radio galaxies jets are among the most extended and powerful shocks in the universe and are known to be efficient accelerators.…”

Shock acceleration in gamma-ray bursts

“…Concerning the mechanism of acceleration to ultra-high energies, one can list quite a few scenarios, among which: shock acceleration in mildly relativistic internal shocks or at the mildly relativistic reverse shock [77,71,80], Fermi acceleration at the ultra-relativistic external shock [76] (see however [21]), acceleration in relativistic turbulence, either in the internal shock phase [77] or behind the external forward shock [81], shear acceleration in the inner jet [4] or through repeated interactions with shock fronts in the internal shock phase [82,83]. Most of these models conclude to the possibility of pulling protons up to the 10 20 eV limit, at the price of more or less optimistic hypotheses.…”

“…If acceleration takes place at short radii, the opacity to pion production must be sufficient to allow the protons to escape the flow by turning into neutrons via photo-hadronic interactions, otherwise the protons would lose their energy through adiabatic expansion (unless the magnetization drops abruptly beyond the acceleration region, see [82] for a discussion). Therefore, the generation of a PeV neutrino signal is a generic prediction of models that accelerate ultra-high energy cosmic rays in the inner parts of gamma-ray bursts.…”