Probing the EBL evolution at high redshift using GRBs detected with the Fermi-LAT

TL;DR

This study uses Fermi-LAT observations of 22 high-redshift gamma-ray bursts to detect EBL attenuation, providing new constraints on the UV component of the extragalactic background light at redshift ~1.8.

Contribution

First detection of EBL attenuation in stacked GRB spectra at high redshift, offering novel constraints on EBL evolution and UV background.

Findings

Marginal EBL attenuation detection at ~2.8 sigma

Constraints on EBL at redshift ~1.8

Fermi-LAT's role in constraining UV EBL component

Abstract

The extragalactic background light (EBL), from ultraviolet to infrared wavelengths, is predominantly due to emission from stars, accreting black holes and reprocessed light due to Galactic dust. The EBL can be studied through the imprint it leaves, via $\gamma$-$\gamma$ absorption of high-energy photons, in the spectra of distant $\gamma$-ray sources. The EBL has been probed through the search for the attenuation it produces in the spectra of BL Lacertae (BL Lac) objects and individual $\gamma$-ray bursts (GRBs). GRBs have significant advantages over blazars for the study of the EBL especially at high redshifts. Here we analyze a combined sample of twenty-two GRBs, detected by the Fermi Large Area Telescope between 65 MeV and 500 GeV. We report a marginal detection (at the ~2.8 $\sigma$ level) of the EBL attenuation in the stacked spectra of the source sample. This measurement represents a first constraint of the EBL at an effective redshift of ~1.8. We combine our results with prior EBL constraints and conclude that Fermi-LAT is instrumental to constrain the UV component of the EBL. We discuss the implications on existing empirical models of EBL evolution.