Overall Ultra-high Energy Neutrino Emission from GRBs during Jet Expansion

TL;DR

This paper models the time-integrated ultra-high-energy neutrino emission from GRB jets during expansion, revealing that neutrino production at larger radii significantly increases the expected fluence and alters flavor ratios, impacting future observations.

Contribution

It introduces a comprehensive numerical model of neutrino spectra during GRB jet expansion, accounting for evolving cosmic ray and secondary particle spectra, which enhances predictions of UHE neutrino fluence.

Findings

Neutrino production at larger radii can dominate high-energy emission.

The overall UHE neutrino fluence is significantly larger than previous estimates.

Neutrino flavor ratios vary with energy due to production at different radii.

Abstract

The ultra-relativistic jet released in gamma-ray bursts (GRBs) is expected to produce ultra-high-energy cosmic rays (UHECRs), prompt gamma-ray emission and hence prompt high-energy neutrinos by photopion interactions. In this work, we calculate the time-integrated neutrino spectrum during the expansion of jets by taking into account the time evolution of cosmic ray and secondary spectra and neutrino production. We numerically solve the continuity equations for nucleons, pions, and muons for their spectral evolution. Since pion and muon damping weakens as the jet expands, the neutrino production at large radii at high energies may dominate that around the jet energy dissipation radius. Compared with the usually adopted approaches that only consider neutrino production around the energy dissipation radius, the overall UHE neutrino fluence integrated over time can be significantly larger, and the flavor fraction of electron neutrinos as function of neutrino energy is different at UHE, due to neutrino production at radii much larger than the energy dissipation radius. The faster magnetic field decay leads to larger UHE neutrino fluence, and the UHE neutrino spectra is weakly dependent on the energy dissipation radius and the jet Lorentz factor. Observations of prompt EeV neutrinos from GRBs by the next-generation neutrino telescopes, e.g., GRAND and IceCube-Gen2, will test the hypothesis of GRBs as UHECR sources and probe the physics of GRB jets.