Radiative Properties of Plasmoids and Plasmoid Mergers in Magnetic Reconnection

TL;DR

This study develops a new image processing method to analyze the radiative properties of plasmoids and their mergers in magnetic reconnection, revealing how mergers influence flares, polarization, and spectral features.

Contribution

It introduces a novel technique combining magnetic vector potential and density to distinguish radiation sources, enabling statistical analysis of plasmoid and merger radiative properties.

Findings

Isolated plasmoids have similar emissivity regardless of size.

Flares from mergers are inversely related to plasmoid size ratio.

Significant spectral hardening and polarization angle variations occur mainly in mergers of comparable-sized plasmoids.

Abstract

Magnetic reconnection is often considered as the primary particle acceleration mechanism in a magnetized blazar zone environment. The majority of radiation in the reconnection layer comes from plasmoids and their mergers. In particular, plasmoid mergers can produce strong multi-wavelength flares and major variations in synchrotron polarization signatures. However, radiative properties of plasmoid mergers have not been well explored due to difficulties in tracking the merging processes. Here we use an image processing method that combines the magnetic vector potential and density to identify isolated and merging plasmoids. We find that this method can clearly distinguish radiation contributions from isolated plasmoids, merging plasmoids, and the primary current sheet of reconnection. This new method enables us to study the radiative properties of plasmoids and mergers statistically. Our results show that isolated plasmoids have similar emissivity regardless of their sizes, and they generally have nonzero polarization degree (PD) due to their quasi-circular shape. Flares due to plasmoid mergers have relative amplitudes that are anti-proportional to the size ratio of the plasmoids participating in the mergers. Finally, only mergers between plasmoids of comparable sizes (width ratio $\lesssim 5$) can lead to significant spectral hardening and polarization angle (PA) variations; the amplitude of the PA variations is between 0 and $180^{\circ}$ and has a mean value of $90^{\circ}$. Our analyses on 2D simulations can pave the way for future analyses and machine learning techniques on radiative properties of 3D magnetic reconnection simulations.