The possibility of multi-TeV secondary gamma rays from GRB221009A

TL;DR

This paper explains the multi-TeV gamma rays from GRB221009A as secondary emissions from cosmic ray interactions, suggesting very weak extragalactic magnetic fields and supporting high-energy cosmic ray acceleration in GRB jets.

Contribution

It demonstrates that secondary gamma rays can account for the observed high-energy flux, challenging the need for nonphysical source spectra and providing insights into extragalactic magnetic fields.

Findings

Secondary gamma rays explain the observed flux.

Extragalactic magnetic fields are constrained to be ≤10^{-16} G.

Supports high-energy cosmic ray acceleration in GRB jets.

Abstract

The brightest gamma ray burst (GRB) ever observed, GRB221009A, produced a surprisingly large flux of gamma rays with multi-TeV energies, which are expected to be absorbed in interactions with extragalactic background light (EBL). If the highest energy gamma rays were produced at the source, their spectral shape would have to exhibit a nonphysical spike even for the lowest levels of EBL. We show that, for widely accepted models of EBL, the data can be explained by secondary gamma rays produced in cosmic ray interactions along the line of sight, as long as the extragalactic magnetic fields along the line of sight are $10^{-16}$G or smaller, assuming 1 Mpc correlation length. Our interpretation supports the widely held expectation that GRB jets can accelerate cosmic rays to energies as high as 10 EeV and above, and it has implications for understanding the magnitudes of EGMFs.