Abstract
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 ∼10 per cent for the host 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 such associated 21-cm absorption signals for strong bursts of ≳several Jy peak flux densities.
Highlights
Fast radio bursts (FRBs), a recently discovered class of transient events in which a ∼ 1 Jy signal of duration ∼ 1 ms is observed at radio frequencies of ∼ 1 − 10 GHz, have become the source of great debate in the astrophysical community
We have proposed a novel method for measuring the cosmological distances to FRBs, based on the 21-cm absorption signature of HI gas in the FRB progenitor’s host galaxy
Using a simple exponential disk model for both FRB and HI galactic distributions we find a probability of ∼ 10% for measuring values of τ ∆v larger than 10 km s−1, and a median value of ∼ 1 km s−1
Summary
Fast radio bursts (FRBs), a recently discovered class of transient events in which a ∼ 1 Jy signal of duration ∼ 1 ms is observed at radio frequencies of ∼ 1 − 10 GHz, have become the source of great debate in the astrophysical community. Loeb lengths λobs yields an estimated measurement of the FRB progenitor’s redshift, z = (λobs/21.106 cm) − 1 The precision of this method is not limited by the unknown electron column density along line-of-sight, in sharp contrast to DM estimates of the distance scale. Our estimates indicate that associated absorption is more likely to yield high HI column densities. It follows that the main contribution to HI absorption originates from the CNM This is because the average column densities NHI = f nHI ds through either the CNM or the WNM are of the same order of magnitude, whereas the T −1 falloff in Eq (1) favors the lower temperature CNM. We calculate the probability of measuring various values of τ ∆v, taking these factors into account
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