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

TL;DR

This paper empirically estimates the Galactic contribution to dispersion measures of extragalactic fast radio bursts using multi-wavelength data, providing model-independent, more accurate values that account for hot gas in the Galaxy.

Contribution

It introduces a novel empirical method to measure Galactic dispersion measure contributions without relying on galaxy models, improving accuracy over previous estimates.

Findings

Median $DM_{Gal}$=64$^{+20}_{-23}$ cm$^{-3}$ pc.

$DM_{Gal}$ shows no clear trend with galactic coordinates.

Provides a publicly available table and code for $DM_{Gal}$ estimation.

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-ray absorption. We improve upon the measurements of N(\oviin) and f$_{OVII}$ compared to previous studies, thus providing a better estimate of the hot phase contribution. 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+spherical halo models. Our measurements provide more complete and accurate estimates of $DM_{Gal}$ independent from the previous studies. We provide a table and a code to retrieve $DM_{Gal}$ for any FRB localized in the sky.