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 showthat the 21-cmabsorption line of hydrogen can be used to infer the redshifts of FRB sources, and determinewhether they are Galactic or extragalactic. We calculate a probability of 10 per cent for thehost galaxy of an FRB to exhibit a 21-cm absorption feature of equivalent width ≲10 km s-1.Arecibo, along with several future radio observatories, should be capable of detecting suchassociated 21-cm absorption signals for strong bursts of ≲several Jy peak flux densities.