Gamma-Ray Bursts, Cosmic-Rays and Neutrinos

Abstract

The gamma-ray burst (GRB) model for production of ultra-high-energy cosmic-rays (UHECRs) is based on the hypothesis that GRBs arise from the dissipation of the kinetic energy of relativistic fireballs at cosmological distances. Recent GRB afterglow observations support the validity of this hypothesis and provide quantitative support for the model. The inferred physical fireball parameters imply that protons may be accelerated to >10^20 eV, and the inferred GRB energy generation rate is similar to that required to account for the observed flux of UHECRs. Strong suppression of UHECR flux is expected in this model above 10^19.7 eV, due to proton interaction with CMB photons. Strong deviations from model flux derived under the assumption of uniform source distribution is expected above 10^20 eV, due to source clustering. The flux above 10^20.5 eV is expected to be dominated by few, narrow spectrum sources. While model predictions can not be tested (with high confidence level) at present, the predicted signatures should be observed with the planned Auger and Telescope-Array UHECR detectors. A natural consequence of the GRB model of UHECR production is the conversion of a large fraction, ~10%, of the fireball energy to accompanying burst of \~10^14 eV and ~10^18 eV neutrinos. A km^2 neutrino detector would observe several tens of events per year correlated with GRBs, and test for neutrino properties (e.g. flavor oscillations, for which upward moving tau's would be a unique signature, and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible.