The Twisting of Radio Waves in a Randomly Inhomogeneous Plasma

TL;DR

This paper introduces and analyzes a geometric depolarization mechanism affecting radio waves traveling through turbulent plasma, which impacts astrophysical polarization observations and interpretations.

Contribution

It provides a theoretical framework for geometric depolarization (GDP) in randomly inhomogeneous plasma, highlighting its significance in astrophysical radio wave propagation.

Findings

GDP causes significant depolarization in turbulent plasma

The effect is crucial for interpreting polarization in fast radio bursts

GDP cannot be ignored in astrophysical polarization analysis

Abstract

Polarization of electromagnetic waves carries a large amount of information about their astrophysical emitters and the media they passed through, and hence is crucial in various aspects of astronomy. Here we demonstrate an important but long-overlooked depolarization mechanism in astrophysics: when the polarization vector of light travels along a non-planar curve, it experiences an additional rotation, in particular for radio waves. The process leads to depolarization, which we call `geometric' depolarization (GDP). We give a concise theoretical analysis of the GDP effect on the transport of radio waves in a randomly inhomogeneous plasma under the geometrical optics approximation. In the case of isotropic scattering in the coronal plasma, we show that the GDP of the angle-of-arrival of the linearly polarized radio waves propagating through the turbulent plasma cannot be ignored. The GDP effect of linearly polarized radio waves can be generalized to astrophysical phenomena, such as fast radio bursts and stellar radio bursts, etc. Our findings may have a profound impact on the analysis of astrophysical depolarization phenomena.