Prospects for detection of the pair-echo emission from TeV gamma-ray bursts

TL;DR

This paper models the delayed pair-echo emission from TeV gamma-ray bursts to assess the potential of gamma-ray observations in constraining the intergalactic magnetic field strength, highlighting observational strategies for current and future instruments.

Contribution

It introduces a phenomenological model based on recent GRB observations to predict pair-echo emission and evaluates detection prospects for probing the intergalactic magnetic field.

Findings

Extending observations for at least 3 hours enhances IGMF detection prospects.

GeV-TeV observations of GRBs can effectively probe IGMF strengths of 10^{-17} to 10^{-19} G.

Detection strategies can be optimized for current and upcoming gamma-ray telescopes.

Abstract

The intergalactic magnetic field (IGMF) present in the voids of large-scale structures is considered to be the weakest magnetic field in the Universe. Gamma-ray observations of blazars in the GeV-TeV domain have led to lower limits on the IGMF strength based on the search for delayed or extended emission. Nevertheless, these results have been obtained with strong assumptions placed on the unknown source properties. The recent discovery of TeV radiation from gamma-ray bursts (GRBs) has paved the way for IGMF studies with these bright transients. Among the current TeV-detected GRBs, GRB 190114C, located at a redshift of $z = 0.42$, is the best sampled. Therefore, it can be considered to be representative of the properties of GRBs in the VHE domain. In addition, GRB 221009A ($z = 0.151$) is the brightest event ever detected. We present a phenomenological model based on the intrinsic properties of GRB 190114C and GRB 221009A to predict the delayed emission component (pair-echo) in the GeV-TeV band. We investigate the detectability of this component from low-redshift ($z \leq 1$) GRBs for three values of IGMF strength ($10^{-19}$ G, $10^{-18}$ G and $10^{-17}$ G), different observational times ($3$ hrs, $6$ hrs, and $9$ hrs) and source intrinsic properties. We find that for current and future generation $\gamma$-ray instruments, extending the observation for at least 3 hours after the GRB detection is a viable strategy for probing the IGMF. We also confirm that GeV-TeV observations of GRBs can probe IGMF strengths on the order of $10^{-17} -10^{-19}$ G, representing a competitive alternative to the current studies performed with active galactic nuclei (AGNs).