Circular Polarization in two Active Repeating Fast Radio Bursts

TL;DR

This study reports the detection of circular polarization in two active repeating FRBs, suggesting intrinsic emission mechanisms or Faraday conversion, and expanding the understanding of polarization properties in these cosmic phenomena.

Contribution

First detection of circular polarization in two active repeating FRBs, increasing the known cases and providing insights into their emission mechanisms.

Findings

Circular polarization detected in FRBs 20121102A and 20190520B.

One burst shows 64% circular polarization.

Circular polarization likely intrinsic or due to Faraday conversion, not multipath effects.

Abstract

Fast radio bursts (FRBs) are bright millisecond radio bursts at cosmological distances. Only a small fraction of FRBs apparently repeat. Polarization, a fundamental property of electromagnetic signals, often carries critical information about the radiation processes, the environment, and the intervening medium of FRBs. Here we report circular polarization detections of two active repeating FRBs, namely FRBs 20121102A and 20190520B, with the Five-hundred-meter Aperture Spherical radio Telescope. We detect circular polarization in both active repeating FRBs, which increases the number of repeating FRBs with circular polarization to three. In one of the bursts of FRB 20121102A, we detect 64% degree of circular polarization. The observed circular polarization is unlikely induced by multipath propagation. Our observations favor circular polarization induced by Faraday conversion or radiation mechanism intrinsic to the FRB source. The conditions to generate circular polarization have to be rare in either case.