Modeling gamma-ray burst observations by Fermi and MAGIC including attenuation due to diffuse background light

TL;DR

This paper models gamma-ray burst observations by Fermi and MAGIC, considering attenuation by diffuse background light, to evaluate their potential in probing high-redshift universe and the extragalactic background light.

Contribution

It introduces a phenomenological model for GRB detection at GeV energies, incorporating EBL interactions and estimating observable photon counts for Fermi and MAGIC.

Findings

Fermi LAT can observe a few high-energy photons annually from distant GRBs.

Ground-based MAGIC observations are highly variable but could detect hundreds of photons from bright GRBs.

Detection of high-redshift GRBs can constrain both GRB physics and the evolving EBL.

Abstract

Gamma rays from extragalactic sources are attenuated by pair-production interactions with diffuse photons of the extragalactic background light (EBL). Gamma-ray bursts (GRBs) are a source of high-redshift photons above 10 GeV, and could be therefore useful as a probe of the evolving UV background radiation. In this paper, we develop a simple phenomenological model for the number and redshift distribution of gamma-ray bursts that can be seen at GeV energies with the Fermi satellite and MAGIC atmospheric Cherenkov telescope. We estimate the observed number of gamma rays per year, and show how this result is modified by considering interactions with different realizations of the evolving EBL. We also discuss the bright Fermi GRB 080916C in the context of this model. We find that the LAT on Fermi can be expected to see a small number of photons above 10 GeV each year from distant GRBs. Annual results for ground-based instruments like MAGIC are highly variable due to the low duty cycle and sky coverage of the telescope. However, successfully viewing a bright or intermediate GRB from the ground could provide hundreds of photons from high redshift, which would almost certainly be extremely useful in constraining both GRB physics and the high-redshift EBL.