The Future of High-Redshift Gamma-Ray Bursts as Probes of the Epoch of Reionization

The Epoch of Reionization (EoR) is a key era of cosmological history in which the light from the first galaxies and stars ionized the intergalactic medium (IGM). While the EoR is theorized to have ended around a redshift of z ~ 5.5 - 6, the main drivers of the EoR and its progression are still debated. Gamma-ray bursts (GRBs) are excellent probes of the EoR. Their extreme luminosities allow them to be detected out to high redshifts, and their relatively simple power-law spectra make them ideal for studying absorption features from their host galaxies and the IGM. GRB spectra can provide estimates of the fraction of neutral hydrogen (i.e., neutral fraction) in the IGM surrounding the GRB host galaxy, which directly traces the progress of the EoR at different redshifts. However, to date only a few high-redshift GRB spectra of high-enough quality to measure the neutral fraction have been obtained. New and upcoming observatories such as JWST and the Extremely Large Telescope (ELT) can supply more high-quality high-redshift GRB spectra, allowing for more precise neutral fraction estimates and improving our understanding of the EoR. We use simulated high-redshift GRB spectra from JWST NIRSpec and ELT HARMONI to examine their capabilities for retrieving the neutral fraction. We find that despite the slow follow-up of JWST and the presence of telluric lines in ELT data, both instruments will be effective at measuring the neutral fraction, and can improve on current constraints on the EoR.