Depolarization and Faraday effects in AGN Jets

TL;DR

This paper generalizes the understanding of depolarization and Faraday effects in AGN jets, showing how magnetic field structures influence polarization and rotation measures, aiding in jet magnetic field analysis.

Contribution

It introduces generalized models of depolarization considering non-uniform magnetic fields, extending Burn's relation for better interpretation of AGN jet polarization data.

Findings

Magnetic field structure influences polarization frequency dependence.

Generalized relations improve interpretation of Faraday rotation in jets.

Magnetic field configurations can be estimated from polarization data.

Abstract

Radio interferometric observations of Active Galactic Nuclei (AGN) jets reveal the significant linear polarization of their synchrotron radiation that changes with frequency due to the Faraday rotation. It is generally assumed that such depolarization could be a powerful tool for studying the magnetized plasma in the vicinity of the jet. However, depolarization could also occur within the jet if the emitting and rotating plasma are co-spatial (i.e. the internal Faraday rotation). Burn obtained very simple dependence of the polarization on the wavelength squared for the discrete source and resolved slab that is widely used for interpreting the depolarization of AGN jets. However it ignores the influence of the non-uniform large scale magnetic field of the jet on the depolarization. Under the simple assumptions about the possible jet magnetic field structures we obtain the corresponding generalizations of Burn's relation widely used for galaxies analysis. We show that the frequency dependencies of the Faraday rotation measure and polarization angle in some cases allow to estimate the structures of the jets magnetic fields.