Polarization properties of 28 repeating fast radio burst sources with CHIME/FRB

TL;DR

This study analyzes the polarization and rotation measure variations in 28 repeating fast radio burst sources observed by CHIME/FRB, revealing two categories of repeaters with distinct RM environments and new insights into their magnetic properties.

Contribution

It provides the first extensive RM measurements for multiple repeating FRBs, identifying two classes based on RM stability and exploring their magnetic environments and temporal RM variations.

Findings

Repeaters split into stable and dynamic RM environment groups.

Temporal RM variations are observed in nearly all repeaters.

Some repeaters show RM sign changes, indicating complex magnetic environments.

Abstract

As part of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) project, we report 41 new Rotation Measures (RMs) from 20 repeating Fast Radio Bursts (FRBs) obtained between 2019 and 2023 for which no previous RM was determined. We also report 22 additional RM measurements for eight further repeating FRBs. We observe temporal RM variations in practically all repeating FRBs. Repeaters appear to be separated into two categories: those with dynamic and those with stable RM environments, differentiated by the ratios of RM standard deviations over the averaged RM magnitudes. Sources from stable RM environments likely have little RM contributions from the interstellar medium (ISM) of their host galaxies, whereas sources from dynamic RM environments share some similarities with Galactic pulsars in eclipsing binaries but appear distinct from Galactic centre solitary pulsars. We observe a new stochastic, secular, and again stochastic trend in the temporal RM variation of FRB 20180916B, which does not support binary orbit modulation being the reason for this RM changes. We highlight two more repeaters that show RM sign change, namely FRBs 20290929C and 20190303A. We perform an updated comparison of polarization properties between repeating and non-repeating FRBs, which show a marginal dichotomy in their distribution of electron-density-weighted parallel-component line-of-sight magnetic fields.