Simulating the 21cm forest detectable with LOFAR and SKA in the spectra of high-z GRBs

TL;DR

This study assesses the potential to detect 21cm absorption features in high-redshift GRB afterglows using LOFAR and SKA, highlighting the conditions under which such signals are observable amidst cosmic reionization.

Contribution

It provides the first detailed simulation-based analysis of 21cm forest detectability in high-z GRB spectra with current and upcoming radio telescopes.

Findings

Detection feasible for PopIII star-originated GRBs at z>7 with LOFAR.

SKA1-low could improve detection prospects by reducing noise.

Standard GRBs remain too dim for detection even with enhanced SKA sensitivity.

Abstract

We investigate the feasibility of detecting 21cm absorption features in the afterglow spectra of high redshift long Gamma Ray Bursts (GRBs). This is done employing simulations of cosmic reionization, together with the instrumental characteristics of the LOw Frequency ARray (LOFAR). We find that absorption features could be marginally (with a S/N larger than a few) detected by LOFAR at z>7 if the GRB originated from PopIII stars, while the detection would be easier if the noise were reduced by one order of magnitude, i.e. similar to what is expected for the first phase of the Square Kilometer Array (SKA1-low). On the other hand, more standard GRBs are too dim to be detected even with ten times the sensitivity of SKA1-low, and only in the most optimistic case can a S/N larger than a few be reached at z>9.