High-energy cosmic-ray nuclei from high- and low-luminosity gamma-ray bursts and implications for multi-messenger astronomy

TL;DR

This paper explores how gamma-ray bursts, both high- and low-luminosity types, can accelerate heavy nuclei to ultra-high energies, and discusses the implications for multi-messenger astronomy and cosmic-ray origins.

Contribution

It demonstrates that heavy nuclei can be accelerated in GRBs and analyzes the conditions for their survival and detection, considering both high- and low-luminosity GRBs.

Findings

Heavy nuclei can reach ultra-high energies in GRB shock models.

Conditions for heavy nuclei survival align with gamma-ray and neutrino escape conditions.

Multi-messenger observations can distinguish contributions of different GRB types to UHECRs.

Abstract

Gamma-ray bursts (GRBs) are one of the candidates of ultra-high-energy (around 10^18.5 eV) cosmic-ray (UHECR) sources. We investigate high-energy cosmic-ray acceleration including heavy nuclei in GRBs by using Geant 4, and discuss its various implications, taking both of high-luminosity (HL) and low-luminosity (LL) GRBs into account. This is because LL GRBs may also make a significant contribution to the observed UHECR flux if they form a distinct population. We show that not only protons but also heavier nuclei can be accelerated up to ultra-high energies in the internal, (external) reverse and forward shock models. We also show that the condition for ultra-high-energy heavy nuclei such as iron to survive is almost the same as that for about TeV gamma-rays to escape from the source and for high-energy neutrinos not to be much produced. The multi-messenger astronomy by neutrino and GeV-TeV gamma-ray telescopes such as IceCube and KM3Net, GLAST and MAGIC will be important to see whether GRBs can be accelerators of ultra-high-energy heavy nuclei. We also demonstrate expected spectra of high-energy neutrinos and gamma rays, and discuss their detectabilities. In addition, we discuss implictaions of the GRB-UHECR hypothesis. We point out, since the number densities of HL-GRBs and LL-GRBs are quite different, its detemination by UHECR observations is also important.