Inferring the distances of fast radio bursts through associated 21-cm absorption

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 similar to 10 per cent for the host galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width greater than or similar to 10 km s(-1). Arecibo, along with several future radio observatories, should be capable of detecting such associated 21-cm absorption signals for strong bursts of greater than or similar to several Jy peak flux densities.