Ultrahigh-Energy Cosmic Ray Production by Turbulence in Gamma-Ray Burst Jets and Cosmogenic Neutrinos

TL;DR

This paper introduces a new model where turbulence in gamma-ray burst jets accelerates protons to ultrahigh energies, producing a hard cosmic-ray spectrum and distinctive neutrino signals, with implications for future observations.

Contribution

The model demonstrates a novel turbulence-based acceleration mechanism in GRB jets that can explain UHECRs and predicts unique neutrino signatures.

Findings

UHECRs can be produced by turbulence in GRB jets after prompt emission.

The resulting UHECR spectrum is very hard, concentrating energy at high energies.

The model predicts a distinctive hard spectrum of cosmogenic neutrinos in the 10^{17}-10^{18} eV range.

Abstract

We propose a novel model to produce ultrahigh-energy cosmic-rays (UHECRs) in gamma-ray burst jets. After the prompt gamma-ray emission, hydrodynamical turbulence is excited in the GRB jets at or before the afterglow phase. The mildly relativistic turbulence stochastically accelerates protons. The acceleration rate is much slower than the usual first-order shock acceleration rate, but in this case it can be energy-independent. The resultant UHECR spectrum is so hard that the bulk energy is concentrated in the highest energy range, resulting in a moderate requirement for the typical cosmic ray luminosity of $\sim 10^{53.5}~\mbox{erg}~\mbox{s}^{-1}$. In this model, the secondary gamma-ray and neutrino emissions initiated by photopion production are significantly suppressed. Although the UHECR spectrum at injection shows a curved feature, this does not conflict with the observed UHECR spectral shape. The cosmogenic neutrino spectrum in the $10^{17}$--$10^{18}$ eV range becomes distinctively hard in this model, which may be verified by future observations.