The Statistical Polarization Properties of Coherent Curvature Radiation by Bunches: Application to Fast Radio Burst Repeaters

TL;DR

This paper models the polarization properties of coherent curvature radiation in repeating FRBs, revealing how line-of-sight deviations influence circular polarization and flux, and analyzing polarization angle behaviors.

Contribution

It introduces a statistical simulation framework for polarization in coherent curvature radiation, explaining observed polarization features in repeating FRBs.

Findings

High circular polarization correlates with low flux.

Most bursts show flat polarization angle evolution.

Depolarization degrees vary little across wide frequency bands.

Abstract

Fast radio bursts (FRBs) are extragalactic radio transients with millisecond duration and extremely high brightness temperature. Very recently, some highly circularly polarized bursts were found in a repeater, FRB 20201124A. The significant circular polarization might be produced by coherent curvature radiation by bunches with the line of sight (LOS) deviating from the bunch central trajectories. In this work, we carry out simulations to study the statistical properties of burst polarization within the framework of coherent curvature radiation by charged bunches in the neutron star magnetosphere for repeating FRBs. The flux is almost constant within the opening angle of the bunch. However, when the LOS derivates from the bunch opening angle, the larger the derivation, the larger the circular polarization but the lower the flux. We investigate the statistical distribution of circular polarization and flux of radio bursts from an FRB repeater, and find that most of the bursts with high circular polarization have a relatively low flux. Besides, we find that most of the depolarization degrees of bursts have a small variation in a wide frequency band. Furthermore, we simulate the polarization angle (PA) evolution and find that most bursts show a flat PA evolution within the burst phases, and some bursts present a swing of PA.