Empirical estimates of the Galactic halo contribution to the dispersion measures of extragalactic fast radio bursts using X-ray absorption

Abstract

We provide an empirical list of the Galactic dispersion measure (DM Gal ) contribution to the extragalactic fast radio bursts along 72 sightlines. It is independent of any model of the Galaxy, i.e., we do not assume the density of the disk or the halo, spatial extent of the halo, baryonic mass content, or any such external constraints to measure DM Gal . We use 21-cm, UV, EUV and X-ray data to account for different phases, and find that DM Gal is dominated by the hot phase probed by X-rays. The median DM Gal = 64 +20 −23 cm −3 pc, with a 68% (90%) confidence interval of 33-172 (23-660) cm −3 pc. The DM Gal does not appear to follow any trend with the galactic longitude or latitude, and there is a large scatter around the values predicted by simple disk+halo models. Our measurements provide complementary (if not better) estimates of the Galactic DM compared to the previous studies. We provide a table and a code to retrieve DM Gal for any FRB localized in the sky.