Polarization of synchrotron emission from relativistic reconfinement shocks with ordered magnetic fields

TL;DR

This paper models the polarization of synchrotron emission at relativistic reconfinement shocks, considering ordered magnetic fields, revealing how different field configurations influence polarization patterns and their observational signatures.

Contribution

It introduces a detailed calculation of synchrotron polarization incorporating toroidal and helical magnetic fields in relativistic shocks, highlighting their distinct polarization signatures.

Findings

Toroidal fields produce high parallel polarization.

Helical fields cause non-axisymmetric brightness distribution.

Polarization maps reveal flow transition points.

Abstract

We calculate the polarization of synchrotron radiation produced at the relativistic reconfinement shocks, taking into account globally ordered magnetic field components, in particular toroidal and helical fields. In these shocks, toroidal fields produce high parallel polarization (electric vectors parallel to the projected jet axis), while chaotic fields generate moderate perpendicular polarization. Helical fields result in a non-axisymmetric distribution of the total and polarized brightness. For a diverging downstream velocity field, the Stokes parameter U does not vanish and the average polarization is neither strictly parallel nor perpendicular. A distance at which the downstream flow is changing from diverging to converging can be easily identified on polarization maps as the turning point, at which polarization vectors switch, e.g., from clockwise to counterclockwise.