Secondary GeV-TeV emission from ultra-high-energy cosmic rays accelerated by GRB 221009A

TL;DR

This paper explores the possibility that gamma-ray burst GRB 221009A accelerated ultra-high-energy cosmic rays, leading to secondary gamma-ray emissions detectable on Earth, which could reveal properties of intergalactic magnetic fields and UHECR origins.

Contribution

The study interprets early gamma-ray data from GRB 221009A as potential secondary emission from UHECRs, suggesting energies >10^{21} eV and a very weak intergalactic magnetic field, proposing new observational strategies.

Findings

UHECRs from GRB 221009A may have energies >10^{21} eV.

Detected GeV-TeV emission could be secondary from UHECRs.

Intergalactic magnetic field strength along this line of sight is constrained to B ≤ 3×10^{-16} G.

Abstract

The origin of ultra-high-energy cosmic rays (UHECRs) remains elusive. Gamma-ray bursts (GRBs) are among the best candidates able to meet the stringent energy requirements needed for particle acceleration to such high energies. If UHECRs were accelerated by the central engine of GRB 221009A, it might be possible to detect secondary photons and neutrinos as the UHECRs travel from the source to the Earth. Here we attempt to interpret some of the early publicly available data connected to this burst. If the reported early GeV-TeV detection was produced by secondary emission from UHECRs it probably indicates that UHECRs reached energies $> 10^{21}$ eV and that GRB 221009A exploded inside a magnetic void with intergalactic magnetic field (IGMF) strength $B \leq 3 \times 10^{-16}$ G. In order to understand the entire energy deposition mechanism, we propose to search existing and future Fermi-LAT data for secondary emission arriving over larger spatial scales and longer time-scales. This strategy might help clarify the origin of UHECRs, constrain the intergalactic magnetic field (IGMF) strength along this line of sight and start to quantify the fraction of magnetic voids around GRBs.