A First-Principle Model for Polarization Swings during Reconnection-Powered Flares

TL;DR

This paper presents a first-principle model explaining polarization swings during reconnection-powered flares in relativistic jets, supported by particle-in-cell simulations showing how magnetic reconnection accelerates particles and causes polarization rotation.

Contribution

It introduces a novel physical mechanism linking magnetic reconnection to polarization swings during high-energy astrophysical flares, supported by simulation evidence.

Findings

Reconnection accelerates particles at flux rope interfaces.

Particle streaming causes polarization vector rotation.

Reconnection explains observed blazar flare polarization behavior.

Abstract

We show that magnetic reconnection in a magnetically-dominated fast-cooling plasma can naturally produce bright flares accompanied by rotations in the synchrotron polarization vector. With particle-in-cell simulations of reconnection, we find that flares are powered by efficient particle acceleration at the interface of merging magnetic flux ropes, or "plasmoids". The accelerated particles stream through the post-merger plasmoid towards the observer, thus progressively illuminating regions with varying plane-of-sky field direction, and so leading to a rotation in the observed polarization vector. Our results provide evidence for magnetic reconnection as the physical cause of high-energy flares from the relativistic jets of blazars (which recent observations have shown to be frequently associated with polarization rotations), and provide a first-principle physical mechanism for such flares.