# Magnetized Current Filaments as a Source of Circularly Polarized Light

## TL;DR

This paper demonstrates through simulations that magnetized current filaments generated by the Weibel instability can produce circularly polarized light, with polarization levels depending on plasma magnetization and ion-electron mass ratio.

## Contribution

It reveals a novel mechanism linking current filamentation instability to circular polarization in radiation, supported by PIC simulations and applicable to astrophysical and laboratory conditions.

## Key findings

- Circular polarization increases with plasma magnetization.
- Polarization saturates at approximately 13%.
- Effect requires ion-electron mass ratio greater than unity.

## Abstract

We show that the Weibel or currente filamentation instability can lead to the emission of circularly polarized radiation. Using particle-in-cell (PIC) simulations and a radiation post-processing numerical algorithm, we demonstrate that the level of circular polarization increases with the initial plasma magnetization, saturating at ~13% when the magnetization, given by the ratio of magnetic energy density to the electron kinetic energy density, is larger than 0.05. Furthermore, we show that this effect requires an ion-electron mass ratio greater than unity. These findings, which could also be tested in currently available laboratory conditions, show that the recent observation of circular polarization in gamma ray burst afterglows could be attributed to the presence of magnetized current filaments driven by the Weibel or the current filamentation instability.