Probing the Nature of the Weakest Intergalactic Magnetic Fields with the High Energy Emission of Gamma-Ray Bursts

TL;DR

This paper explores how delayed high-energy gamma-ray emissions from gamma-ray bursts can be used to probe the properties of extremely weak intergalactic magnetic fields, considering geometrical effects and different magnetic field configurations.

Contribution

It provides a detailed analysis of the time-dependent spectra of secondary gamma-ray emission, accounting for magnetic field effects, and distinguishes between coherent and tangled magnetic field scenarios.

Findings

Secondary photon flux around 10^{-8} GeV cm^{-2} s^{-1} for z~1

Delay times of about 10^4 seconds for weak magnetic fields

Differences in emission characteristics between magnetic field configurations

Abstract

We investigate the delayed, secondary GeV-TeV emission of gamma-ray bursts and its potential to probe the nature of intergalactic magnetic fields. Geometrical effects are properly taken into account for the time delay between primary high energy photons and secondary inverse Compton photons from electron-positron pairs, which are produced in $\gamma$-$\gamma$ interactions with background radiation fields and deflected by intervening magnetic fields. The time-dependent spectra of the delayed emission are evaluated for a wide range of magnetic field strengths and redshifts. The typical flux and delay time of secondary photons from bursts at $z \sim 1$ are respectively $\sim 10^{-8}$ GeV cm$^{-2}$ s$^{-1}$ and $\sim 10^4$ s if the field strengths are $\sim 10^{-18}$ G, as might be the case in intergalactic void regions. We find crucial differences between the cases of coherent and tangled magnetic fields, as well as dependences on the field coherence length.