Neutrino, Neutron, and Cosmic‐Ray Production in the External Shock Model of Gamma‐Ray Bursts

Abstract

The hypothesis that ultrahigh-energy (e10 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 $1% of the total energy release. The radiative characteristics of the neutron -decay electrons from the GRB '' neutron bomb '' are solved in a special case. Galaxies with GRB activity should be surrounded by radiation halos of $100 kpc extent from the outflowing 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 electron halo from a single GRB with e2 Â 10 53 ergs isotropic energy release is $10 35 ergs s À1 , with a potentially much brighter signal from the neutron decay protons. The decay halo from a single GRB can persist for e0.1-1 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 profile 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 $10 40AE1 ergs s À1 . 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.

High-energy cosmic rays from γ-ray bursts

“…This model extends the work of Vietri (1) and Waxman (2), who proposed that UHECRs originate from GRBs (see also Ref. (3)), to include cosmic ray production from SNe and GRB sources in our Galaxy (4). To test the model, KASCADE (5; 6; 7) and HiRes-I and HiRes-II Monocular data (8) are fit over the energy range ≈ 2×10 16 eV to ≈ 3 × 10 20 eV.…”

“…(4) gives the local GRB emissivity in the form of nonthermal photon radiation to beε 44 ∼ = 0.6. Vietri, de Marco, and Guetta (31) argue for a value ofε 44 ∼ = 1.1.…”

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

“…Though we focus on the impact on cosmogenic neutrino production (as Dermer and Holmes have also recently done for GRB rates directly tracing several SFHs [37]), the metallicity-biased evolution model would also have implications for predictions of diffuse neutrino fluxes directly produced in GRBs (e.g., Refs. [15,38]) and their prospects for detection [39,40].…”

“…Active galactic nuclei (AGN) have long been considered as possible UHECR sources [12]. Relatively recently, a potential connection between gamma-ray bursts (GRBs) and UHECR has been explored [13][14][15]. GRBs, which are now generally accepted to be related to core-collapse supernovae [16], are violent events which release great amounts of energy in the form of gamma-rays ( 10 51 -10 52 erg) [17].…”

Neutrinos from decaying muons, pions, neutrons and kaons in gamma ray bursts

“…Ultrahigh energy neutrons are also produced in pγ interactions along with pions and kaons [25,26]. This channel was considered to estimate TeV neutrino flux from Cygnus OB2 located about 1.7 kpc away from us [39].…”