Neutrino, neutron, and cosmic-ray production in the external shock model of gamma-ray bursts

The hypothesis that ultrahigh-energy (greater than or similar to10(19) eV) cosmic rays ( UHECRs) are accelerated by gamma-ray burst (GRB) blast waves is assumed to be correct. Implications of this assumption are then derived for the external shock model of GRBs. The evolving synchrotron radiation spectrum in GRB blast waves provides target photons for the photomeson production of neutrinos and neutrons. Decay characteristics and radiative efficiencies of the neutral particles that escape from the blast wave are calculated. The diffuse high-energy GRB neutrino background and the distribution of high-energy GRB neutrino events are calculated for specific parameter sets, and a scaling relation for the photomeson production efficiency in surroundings with different densities is derived. GRBs provide an intense flux of high-energy neutrons, with neutron production efficiencies exceeding similar to1% of the total energy release. The radiative characteristics of the neutron beta-decay electrons from the GRB neutron bomb are solved in a special case. Galaxies with GRB activity should be surrounded by radiation halos of similar to100 kpc extent from the out owing neutrons, consisting of a nonthermal optical/X-ray synchrotron component and a high-energy gamma-ray component from Compton-scattered microwave background radiation. The peak luminosity emitted by the diffuse beta electron halo from a single GRB with greater than or similar to2 x 10(53) ergs isotropic energy release is similar to10(35) ergs s(-1), with a potentially much brighter signal from the neutron decay protons. The decay halo from a single GRB can persist for greater than or similar to0.1-1 Myr. Stronger neutrino fluxes and neutron decay halos can be produced by external shocks in clumpy external media and in scenarios involving internal shock scenarios, so detection of neutrinos associated with smooth pro le GRBs could rule out an impulsive GRB central engine and an external shock model for the prompt phase. The luminosity of sources of GRBs and relativistic outflows in L* galaxies such as the Milky Way is at the level of similar to10(40+/-1) ergs s(-1). This is sufficient to account for UHECR generation by GRBs. We briefly speculate on the possibility that hadronic cosmic rays originate from the subset of supernovae that collapse to form relativistic outflows and GRBs.