Polarization of synchrotron emission from relativistic reconfinement shocks

TL;DR

This paper investigates the polarization characteristics of synchrotron emission from relativistic reconfinement shocks with chaotic magnetic fields, revealing how polarization depends on jet geometry and observer angle.

Contribution

It provides a hydrodynamical model and synthetic polarization maps for relativistic reconfinement shocks, explaining polarization patterns based on shock geometry and flow divergence.

Findings

Polarization vectors are parallel near the structure ends for certain angles.

The average polarization degree does not exceed 30%.

Parallel polarization with degrees below 10% occurs under specific conditions.

Abstract

We study the polarization properties of relativistic reconfinement shocks with chaotic magnetic fields. Using our hydrodynamical model of their structure, we calculate synthetic polarization maps, longitudinal polarization profiles and discuss the spatially averaged polarization degree as a function of jet half-opening angle Theta_j, jet Lorentz factor Gamma_j and observer inclination angle to the jet axis theta_{obs}. We find, that for theta_{obs} <= Theta_j the wave electric vectors are parallel in the vicinity of the structure ends and perpendicular in between, while for theta_{obs} > Theta_j the polarization can only be perpendicular. The spatially averaged polarization degree does not exceed 30%. Parallel average polarization, with polarization degrees lower than 10%, have been found for theta_{obs} < Theta_j under the condition Gamma_j * Theta_j > 1. As earlier works predicted the parallel polarization from relativistic conical shocks, we explain our results by discussing conical shocks with divergent upstream flow.