Probing Early Cosmic Magnetic Fields through Pair Echos from High-Redshift GRBs

TL;DR

This paper explores how detecting pair echos from high-redshift gamma-ray bursts can reveal the properties of weak intergalactic magnetic fields during early cosmic epochs, using future gamma-ray observatories.

Contribution

It proposes a novel method to probe early universe magnetic fields through pair echos from high-redshift GRBs, emphasizing detectability with upcoming gamma-ray telescopes.

Findings

Pair echos from high-z GRBs are potentially detectable with future facilities.

Detectability depends on GRB energies, IGMF strength, and intergalactic radiation background.

Observations can provide insights into magnetic fields during early cosmic epochs.

Abstract

We discuss the expected properties of pair echo emission from gamma-ray bursts (GRBs) at high redshifts ($z \gtrsim 5$), their detectability, and the consequent implications for probing intergalactic magnetic fields (IGMFs) at early epochs. Pair echos comprise inverse Compton emission by secondary electron-positron pairs produced via interactions between primary gamma-rays from the GRB and low-energy photons of the diffuse intergalactic radiation, arriving with a time delay that depends on the nature of the intervening IGMFs. At sufficiently high $z$, the IGMFs are unlikely to have been significantly contaminated by astrophysical outflows, and the relevant intergalactic radiation may be dominated by the well-understood cosmic microwave background (CMB). Pair echoes from luminous GRBs at $z \sim 5-10$ may be detectable by future facilities such as the Cherenkov Telescope Array or the Advanced Gamma-ray Imaging System, as long as the GRB primary emission extends to multi-TeV energies, the comoving IGMFs at these redshifts are $B \sim 10^{-16}-10^{-15}~{\rm Gauss}$, and the non-CMB component of the diffuse intergalactic radiation is relatively low. Observations of pair echos from high-$z$ GRBs can provide a unique, in-situ probe of weak IGMFs during the epochs of early structure formation and cosmic reionization.