PREPRINT

The observed polarization direction depending on geometrical and kinematic parameters of relativistic jets

Marina S. Butuzova

Submitted on 3 November 2022

Abstract

The study of the polarization direction is crucial in the issue of restoring the spatial structure of the magnetic field in the active galaxy parsec-scale jets. But, due to relativistic effects, the magnetic field projected onto the celestial sphere in the source reference frame cannot be assumed to be orthogonal to the observed direction of the electric vector in the wave. Moreover, the local axis of the jet component may not coincide with its motion direction, which affects the observed polarization direction. In this article, we analyze the transverse to jet distributions of the electric vector in the wave, obtained as a result of modeling with different jet kinematic and geometrical parameters for a helical magnetic field with a different twist angle and for a toroidal magnetic field in the center, surrounded by a varying thickness sheath, penetrated by a poloidal field. We obtained: 1) the shape of the electric vector transverse distribution depends in a complex way on the angles of the jet axis and the velocity vector with the line of sight; 2) ambiguity in determining the twist direction of the helical magnetic field under using only the distributions of the electric vector in the wave; 3) both considered magnetic field topologies can reproduce both the ``spine-sheath'' polarization structure and individual bright details with the longitudinal to the jet axis polarization direction.

Preprint

Comment: Accepted to Astronomy Reports. 30 figures, 1 table

Subject: Astrophysics - High Energy Astrophysical Phenomena

URL: http://arxiv.org/abs/2211.01790

Types of EV distribution (marked with different symbols) depending on $\theta$ and $\theta_\rho$ for $p=3^\circ$ and $\rho/p=25$. The points forming closed loops \textit{a}, \textit{b} and \textit{c} are obtained for $\theta_0=2$, 5 and 10$^\circ$, respectively, and equidistant values of the azimuth angle. The dotted line is drawn for $\theta_\rho=p$. The angle of the helical magnetic field with the local jet axis is 25$^\circ$ (left) and 65$^\circ$ (right).