Large-Amplitude Blazar Polarization Angle Swing as a Signature of Magnetic Reconnection

TL;DR

This paper demonstrates through simulations that large-amplitude polarization angle swings in blazars can serve as a distinctive observational signature of relativistic magnetic reconnection events in astrophysical plasmas.

Contribution

The study introduces integrated PIC and radiation transfer simulations showing that plasmoid coalescences cause observable polarization swings, linking magnetic reconnection to blazar flare signatures.

Findings

Large polarization angle swings (>180°) can result from magnetic reconnection.

Reconnection events produce variable light curves and polarization degrees.

Simulations match observed blazar flare polarization behaviors.

Abstract

Relativistic magnetic reconnection events can widely exist in magnetized plasmas in astrophysical systems. During this process, oppositely directed magnetic field lines reconnect and release magnetic energy, efficiently accelerating nonthermal particles. However, so far there is little clear observational signatures of relativistic magnetic reconnection events in astrophysical systems. Blazars are relativistic magnetized plasma outflows from supermassive black holes. Their multi-wavelength flares may be powered by relativistic magnetic reconnection. The highly variable radiation and polarization signatures are well covered by multi-wavelength observation campaigns, making them ideal targets to examine the magnetic reconnection model. Recent observations have found that several blazar flares are accompanied by optical polarization angle swings which may be of as large amplitude as $> 180^{\circ}$, challenging existing theoretical models. In this paper, we present integrated particle-in-cell (PIC) and polarized radiation transfer simulations of magnetic reconnection events. We find that plasmoid coalescences in the reconnection layer can give rise to highly variable light curves, low and fluctuating polarization degree, and rotating polarization angle. In particular, large-amplitude polarization angle swings, similar to those observed during blazar flares, can be a unique signature of relativistic magnetic reconnection events.