A Model of Polarisation Rotations in Blazars from Kink Instabilities in Relativistic Jets

TL;DR

This paper models polarization rotations in blazar jets as resulting from kink instabilities, linking them to jet power increases and exploring limitations due to depolarization and viewing angles.

Contribution

It introduces a simple model connecting kink instabilities to polarization rotations and discusses challenges in explaining large rotations in blazars.

Findings

Polarization rotation amplitude is sensitive to viewing angle.

Intrinsic depolarization limits the coherence of polarization rotations.

Current-driven kink modes face obstacles in explaining large rotations.

Abstract

This paper presents a simple model of polarisation rotation in optically thin relativistic jets of blazars. The model is based on the development of helical (kink) mode of current-driven instability. A possible explanation is suggested for the observational connection between polarisation rotations and optical/gamma-ray flares in blazars, if the current-driven modes are triggered by secular increases of the total jet power. The importance of intrinsic depolarisation in limiting the amplitude of coherent polarisation rotations is demonstrated. The polarisation rotation amplitude is thus very sensitive to the viewing angle, which appears to be inconsistent with the observational estimates of viewing angles in blazars showing polarisation rotations. Overall, there are serious obstacles to explaining large-amplitude polarisation rotations in blazars in terms of current-driven kink modes.