# Conversion Measure of Faraday Rotation-Conversion with application to Fast Radio Bursts

## TL;DR

This paper introduces the Conversion Measure as a new way to quantify polarization changes in waves passing through magnetized plasma, providing insights into magnetic field structures in Fast Radio Bursts.

## Contribution

It defines the Conversion Measure for characterizing linear-circular polarization conversion and discusses its potential to reveal magnetic field geometries in FRBs.

## Key findings

- Conversion occurs at localized regions with perpendicular magnetic fields.
- Simultaneous polarization measurements can infer magnetic field structures.
- The method applies to understanding FRB polarization data.

## Abstract

Faraday Rotation-Conversion is the simultaneous rotation of all three Stokes polarization parameters $Q$, $U$, $V$ as an electromagnetic wave propagates through a magnetized plasma. In this regime the Faraday plasma screen is characterized by more than just a Rotation Measure. We define the Conversion Measure that characterizes the wavelength-dependent conversion between the linear and circular polarization. In a cold plasma, the conversion occurs at the localized regions along the wave's path, where the large-scale magnetic field is perpendicular to the propagation direction. The number of these regions along the line of sight through the screen, and their individual contributions to the conversion measure, can be inferred from the polarization measurements. We argue that the simultaneous measurement of wavelength-dependent linear and circular polarization might give an important insight into the magnetic-field geometry of the Faraday screen in FRB121102 and other repeating Fast Radio Bursts.