A Search for Rotation Measure Flare Candidates in Repeating Fast Radio Bursts

TL;DR

This study systematically searches for rapid Rotation Measure (RM) flares in repeating Fast Radio Bursts (FRBs), identifying several candidates that suggest highly dynamic local magnetized environments.

Contribution

It introduces a method to identify RM flare candidates in repeating FRBs and reports multiple potential detections, indicating such flares may be common.

Findings

Identified 2 multi-epoch RM flare candidates in FRB 20121102A and FRB 20201124A.

Found 2 single-epoch candidates in FRB 20180916B.

Results imply RM flares could be frequent among repeating FRBs.

Abstract

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of unknown origin. Rotation measures (RMs) probe their local magneto-ionic environments and provide important clues to their nature. While RM variability has been observed in several repeating FRBs, it is typically gradual or stochastic. Recently, observations of FRB~20220529 revealed an abrupt RM excursion followed by rapid recovery on week-long timescales, termed an ``RM flare'', suggesting a potentially distinct form of RM variability associated with localized magnetized plasma. In this work, we perform a systematic search for RM flare candidates in repeating FRBs with multi-epoch RM measurements. Using a $3\sigma$ significance threshold, we identify two candidates with multiple observational epochs (FRB~20121102A and FRB~20201124A) and two additional single-epoch candidates (FRB~20180916B), in addition to the event in FRB~20220529A. Our results suggest that RM flares, if confirmed, may not be rare among repeating FRBs and point to highly dynamic magnetized environments local to the sources. Future high-cadence polarimetric observations, particularly following the discovery of RM excursions, will be essential for confirming these candidates and constraining their physical origin.