Faraday depolarization and induced circular polarization by multipath propagation with application to FRBs

We describe how the observed polarization properties of an astronomical object are related to its intrinsic polarization properties and the finite temporal and spectral resolutions of the observing device. Moreover, we discuss the effect that a scattering screen, with non-zero magnetic field, between the source and observer has on the observed polarization properties. We show that the polarization properties are determined by the ratio of observing bandwidth and coherence bandwidth of the scattering screen and the ratio of temporal resolution of the instrument and the variability time of screen, as long as the length over which the Faraday rotation induced by the screen changes by similar to pi is smaller than the size of the screen visible to the observer. We describe the conditions under which a source that is 100 per cent linearly polarized intrinsically might be observed as partially depolarized, and how the source's temporal variability can be distinguished from the temporal variability induced by the scattering screen. In general, linearly polarized waves passing through a magnetized scattering screen can develop a significant circular polarization. We apply the work to the observed polarization properties of a few fast radio bursts (FRBs), and outline potential applications to pulsars.

Automated summary

This article describes the relationship between the observed polarization properties of an astronomical object and its intrinsic polarization properties, as well as the finite temporal and spectral resolutions of the observing device. It also discusses the impact of a scattering screen with a non-zero magnetic field on the observed polarization properties. The findings highlight the importance of the observing bandwidth, coherence bandwidth, and temporal resolution in determining the polarization properties.