Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare

TL;DR

This study uses spectropolarimetric data from CoMP to analyze the plasma-sheet dynamics during a major solar flare, revealing small-scale magnetic structures likely caused by plasmoid formation, which impact polarization signals.

Contribution

It provides new insights into magnetic field structures in the solar plasma-sheet during flares using spectropolarimetric observations, highlighting the role of plasmoid formation in magnetic reconnection.

Findings

Small polarization aligned with plasma-sheet indicates complex magnetic structures.

Magnetic field structures below 6 Mm cause depolarization.

Plasmoid formation during reconnection influences polarization signals.

Abstract

We examine spectropolarimetric data from the CoMP instrument, acquired during the evolution of the September 10th 2017 X8.2 solar flare on the western solar limb. CoMP captured linearly polarized light from two emission lines of Fe XIII at 1074.7 and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot plasma-sheet lying above the bright flare loops and beneath the ejected CME. The polarization has a striking and coherent spatial structure, with unexpectedly small polarization aligned with the plasma-sheet. By elimination, we find that small-scale magnetic field structure is needed to cause such significant depolarization, and suggest that plasmoid formation during reconnection (associated with the tearing mode instability) creates magnetic structure on scales below instrument resolution of 6 Mm. We conclude that polarization measurements with new coronagraphs, such as the upcoming DKIST, will further enhance our understanding of magnetic reconnection and development of turbulence in the solar corona.