On the magnetoionic environments of fast radio bursts

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 fast radio bursts (FRBs) by deriving their estimated average magnetic field strengths along the line of sight <B<inf>||</inf>>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 <B<inf>||</inf>>are 1.77^+9.01<inf>-1.48</inf>μG and 1.74^+14.82<inf>-1.55</inf>μG using two different methods, which is slightly larger but not inconsistent with the distribution of Galactic pulsars, 1.00^+1.51<inf>-0.60</inf>μG. Only six Galactic magnetars have estimated<B<inf>||</inf>>. Excluding PSR J1745-2900 that has an anomalously high value due to its proximity with the Galactic Centre, the other five sources have amean value of 1.70 μG, which is statistically consistent with the<B<inf>||</inf>> distributions of both Galactic pulsars and FRBs. There is no apparent trend of evolution of magnetar<B<inf>||</inf>>as a function of age or surface magnetic field strength. Galactic pulsars and magnetars close to the Galactic Centre have relatively larger <B<inf>||</inf>> 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.