# Polarization swings in blazars

## TL;DR

This paper introduces a model explaining blazar polarization variability, capturing both smooth EVPA swings and seemingly random flux and polarization changes through a jet with helical magnetic fields and variable orientation.

## Contribution

It presents a novel model linking jet dynamics and magnetic fields to diverse polarization behaviors observed in blazars, including large EVPA swings and polarization fraction variability.

## Key findings

- EVPA can undergo large smooth variations with variable polarization fraction
- Polarization fraction can be near zero during 90° EVPA jumps or remain constant during smooth swings
- Total EVPA rotation can be arbitrarily large

## Abstract

We present a model of blazar variability that can both reproduce smooth large polarization angle swings, and at the same time allow for the seemingly random behaviour of synchrotron fluxes, polarization fraction and, occasionally, $\pi$/2 polarization jumps. We associate blazar flaring activity with a jet carrying helical magnetic fields and propagating along a variable direction (and possibly with a changing bulk Lorentz factor). The model predicts that for various jet trajectories (i) EVPA can experience large smooth temporal variations while at the same time polarization fraction ($\Pi$) can be highly variable; (ii) $\Pi \sim 0$ near sudden EVPA jumps of 90$^{\circ}$, but can also remain constant for large, smoother EVPA swings; (iii) the total angle of EVPA rotation can be arbitrary large; (iv) intensity I is usually maximal at points of fastest EVPA changes, but can have a minimum. Thus, even for a regular, deterministic motion of a steadily emitting jet the observed properties can vary in a non-monotonic and/or seemingly stochastic way. Intrinsic fluctuations of the emissivity will further complicated the intensity profiles, but are expected to preserve the polarization structure.