Neutral hydrogen absorption towards Fast Radio Bursts

TL;DR

This paper explores the potential of using neutral hydrogen absorption features to independently confirm the cosmological distances of Fast Radio Bursts, leveraging current and upcoming radio telescope capabilities.

Contribution

It proposes a method to determine FRB distances through HI absorption detection, offering an independent verification of their cosmological origin.

Findings

Absorption against galactic spiral arms detectable with existing facilities.

SKA can detect extragalactic HI absorption in a few percent of FRBs at z~1.

Potential for confirming FRB distances independently of dispersion measures.

Abstract

If Fast Radio Bursts (FRBs) are truly at astronomical, in particular cosmological, distances, they represent one of the most exciting discoveries in astrophysics of the past decade. However, the distance to FRBs has, to date, been estimated purely from their excess dispersion, and has not been corroborated by any independent means. In this paper we discuss the possibility of detecting neutral hydrogen absorption against FRBs both from spiral arms within our own galaxy, or from intervening extragalactic HI clouds. In either case a firm lower limit on the distance to the FRB would be established. Absorption against galactic spiral arms may already be detectable for bright low-latitude bursts with existing facilities, and should certainly be so by the Square Kilometre Array (SKA). Absorption against extragalactic HI clouds, which would confirm the cosmological distances of FRBs, should also be detectable with the SKA, and maybe also Arecibo. Quantitatively, we estimate that SKA1-MID should be able to detect extragalactic HI absorption against a few percent of FRBs at a redshift z~1.