The propagation-induced circular polarization of fast radio bursts in relativistic plasma

TL;DR

This paper proposes that the circular polarization observed in fast radio bursts results from propagation effects in relativistic plasma within magnetospheres, explaining the variability and rarity of high CP in observations.

Contribution

It introduces a novel model attributing FRB circular polarization to magnetospheric propagation effects in relativistic plasma, challenging previous intrinsic or out-of-magnetosphere explanations.

Findings

High CP occurs under specific plasma conditions, which are rare.

The model explains both high and low CP, including handedness variations.

It aligns with observed rapid polarization changes in FRBs.

Abstract

Although the physical origin of fast radio bursts (FRBs) remains unknown, magnetars are the most likely candidates. The polarization properties of FRBs offer crucial insights into their origins and radiation mechanisms. Significant circular polarization (CP) has been observed in some FRBs. CP may result from intrinsic radiation or propagation effects, both within and outside the magnetosphere. Recent observations indicate that polarization properties of FRB 20201124A can change over short timescales (about tens of milliseconds), challenging models that attribute CP to out-of-magnetosphere emission and propagation. Additionally, some magnetospheric radiation models predict that bursts with high CP produced by off-axis emission will be systematically fainter, which contradicts the observations. We propose that CP arises from magnetospheric propagation effects caused by relativistic plasma. We identify the conditions under which high CP occurs, finding it to be rare. Moreover, our model accounts for the more commonly observed low CP and the varying handedness of CP.