Time-Variable Linear Polarization as a Probe of the Physical Conditions in the Compact Jets of Blazars

TL;DR

This paper discusses how time-variable linear polarization measurements in blazar jets can reveal the magnetic field structure and physical processes like turbulence, reconnection, and particle acceleration, through observations and simulations.

Contribution

It introduces the TEMZ model simulation demonstrating how turbulent and toroidal magnetic fields produce observed polarization variability in blazar jets.

Findings

Polarization patterns vary from systematic to random in blazars.

Simulations show turbulence and magnetic field geometry influence polarization variability.

The TEMZ model reproduces observed polarization behavior in blazar jets.

Abstract

A single measurement of linear polarization of a nonthermal source provides direct information about the mean direction and level of ordering of the magnetic field. Monitoring of the polarization in blazars, combined with millimeter-wave VLBI imaging in both total and polarized intensity, has the potential to determine the geometry of the magnetic field. This is a key probe of the physical processes in the relativistic jet, such as ordered field components, turbulence, magnetic reconnections, magnetic collimation and acceleration of the jet flow, particle acceleration, and radiative processes that produce extremely luminous, highly variable nonthermal emission. Well-sampled monitoring observations of multi-waveband flux and radio-optical polarization of blazars show a variety of behavior. In some cases, the observed polarization patterns appear systematic, while in others randomness dominates. Explanations involve helical magnetic fields, turbulence, and perhaps particle acceleration that depends on the angle between the magnetic field and shock fronts that might be present. Simulations from the author's TEMZ model, with turbulent plasma crossing a standing conical shock in the jet, show that a mixture of turbulent and toroidal magnetic field can produce the level of polarization variability that is observed, even when the two field components are roughly equal.