On the magnetoionic environments of fast radio bursts

TL;DR

This study estimates the magnetic environments of fast radio bursts (FRBs) using Faraday rotation and compares them with Galactic pulsars and magnetars, providing insights into their origins and local environments.

Contribution

It introduces methods to estimate the magnetic field strengths along the line of sight of FRBs and compares these with Galactic sources, informing models of FRB environments.

Findings

FRB magnetic fields are similar to those of Galactic pulsars.

Magnetar environments show no clear evolution with age or magnetic field.

Galactic Center sources tend to have higher magnetic field estimates.

Abstract

Observations of the Faraday rotation measure, combined with the dispersion measure, can be used to infer the magnetoionic environment of a radio source. We investigate the magnetoionic environments of FRBs by deriving their estimated average magnetic field strengths along the line of sight $\langle B_{\parallel}\rangle$ in their host galaxies and comparing them with those of Galactic pulsars and magnetars. We find that for those FRBs with RM measurements, the mean $\langle B_{\parallel}\rangle$ is $1.77^{+9.01}_{-1.48}\,\rm\mu G$ and $1.74^{+14.82}_{-1.55}\,\rm\mu G$ using two different methods, which is slightly larger but not inconsistent with the distribution of Galactic pulsars, $1.00^{+1.51}_{-0.60}\,\rm\mu G$. Only six Galactic magnetars have estimated $\langle B_{\parallel}\rangle$. Excluding PSR J1745--2900 that has an anomalously high value due to its proximity with the Galactic Centre, the other three sources have a mean value of $1.70\,\rm\mu G$, which is statistically consistent with the $\langle B_{\parallel}\rangle$ distributions of both Galactic pulsars and FRBs. There is no apparent trend of evolution of magnetar $\langle B_{\parallel}\rangle$ as a function of age or surface magnetic field strength. Galactic pulsars and magnetars close to the Galactic Centre have relatively larger $\langle B_{\parallel}\rangle$ values than other pulsars/magnetars. We discuss the implications of these results for the magnetoionic environments of FRB 121102 within the context of magnetar model and the model invoking a supermassive black hole, and for the origin of FRBs in general.