Temporal variability of polarization in blazars

TL;DR

This paper models the polarization variability in blazar jets, explaining complex EVPA rotations and fluctuations through a geometric, deterministic approach involving propagating blobs influenced by jet electromagnetic fields.

Contribution

It introduces a self-consistent, non-turbulent electromagnetic model of blazar jets that accounts for diverse polarization behaviors observed in multiwavelength data.

Findings

Complex polarization patterns can be produced without turbulence.

EVPA rotations can reach 180° or more, matching observations.

Polarization variations can be correlated or uncorrelated with luminosity peaks.

Abstract

We investigate the temporal variability of polarization of synchrotron radiation from blazar jets. Multiwavelength observations revealed high-amplitude rotations of the electric vector position angle (EVPA), both in the optical and in the X-rays. More often, the polarization degree and the EVPA show a seemingly erratic variability. To interpret these observations, we present a geometric and deterministic model in which off-axis, compact emitting features (i.e.,~blobs) propagate along the jet with the local velocity of the flow. The dynamics of the blobs is determined by the jet electromagnetic fields, which are calculated self-consistently using an analytical model of magnetically dominated outflows. The jet is axisymmetric, and its electromagnetic fields do not have a turbulent component. We show that the observed polarization is sensitive to the initial spatial configurations of the blobs. For the same jet structure, we observe several remarkably complex polarization patterns, including large EVPA rotations of $180^{\circ}$ or more in both directions and more erratic fluctuations. Simultaneous high-amplitude variations of the polarization degree and the EVPA can coincide with peaks of the observed luminosity. However, seemingly uncorrelated variations are also possible. We discuss the feasibility of constraining the particle acceleration mechanism from multifrequency polarimetric observations.