Correcting Bandwidth Depolarization by Extreme Faraday Rotation

TL;DR

This paper introduces a new algorithm integrated into RM-Tools that detects and corrects bandwidth depolarization in radio polarization data, improving the accuracy of polarization measurements in the presence of Faraday rotation.

Contribution

The authors derived a simple predictive equation for bandwidth depolarization and developed a novel algorithm that enhances detection and correction of depolarized signals in RM synthesis.

Findings

The new algorithm outperforms conventional methods in signal-to-noise ratio.

It accurately recovers source polarization properties from real LOFAR data.

The method is implemented as a tool in the RM-Tools package.

Abstract

Measurements of the polarization of radio emission are subject to a number of depolarization effects such as bandwidth depolarization, which is caused by the averaging effect of a finite channel bandwidth combined with the frequency-dependent polarization caused by Faraday rotation. There have been very few mathematical treatments of bandwidth depolarization, especially in the context of the rotation measure (RM) synthesis method for analyzing radio polarization data. We have found a simple equation for predicting if bandwidth depolarization is significant for a given observational configuration. We have derived and tested three methods of modifying RM synthesis to correct for bandwidth depolarization. From these tests we have developed a new algorithm that can detect bandwidth-depolarized signals with higher signal-to-noise than conventional RM synthesis and recover the correct source polarization properties (RM and polarized intensity). We have verified that this algorithm works as expected with real data from the LOFAR Two-metre Sky Survey. To make this algorithm available to the community, we have added it as a new tool in the RM-Tools polarization analysis package.