Inferring the Distances of Fast Radio Bursts Through Associated 21-cm Absorption

TL;DR

This paper proposes using 21-cm hydrogen absorption lines to determine the distances and origins of Fast Radio Bursts, distinguishing between Galactic and extragalactic sources.

Contribution

It introduces a method to infer FRB redshifts via 21-cm absorption, providing a new tool for understanding FRB locations and properties.

Findings

Approximately 10% probability of detecting 21-cm absorption in FRB host galaxies.

Detection feasible with current and future radio telescopes for strong bursts.

Method can help classify FRBs as Galactic or extragalactic.

Abstract

The distances of Fast Radio Burst (FRB) sources are currently unknown. We show that the 21-cm absorption line of hydrogen can be used to infer the redshifts of FRB sources, and determine whether they are Galactic or extragalactic. We calculate a probability of $\sim 10\%$ for the host galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width $\gtrsim 10 ~\mathrm{km}~\mathrm{s}^{-1}$. Arecibo, along with several future radio observatories, should be capable of detecting such associated 21-cm absorption signals for strong bursts of $\gtrsim {\rm several}~\mathrm{Jy}$ peak flux densities.