Dynamics of Late-Stage Reconnection in the 2017 September 10 Solar Flare

TL;DR

This study investigates the prolonged magnetic reconnection activity in the 2017 September 10 solar flare using multi-instrument observations, revealing ongoing reconnection processes up to 27 hours after flare onset.

Contribution

It provides the first detailed analysis of late-stage reconnection in a major solar flare, extending understanding of flare evolution beyond the impulsive phase.

Findings

Reconnection signatures persist for over 27 hours after flare onset.

The plasma sheet remains visible in polarization data long after EUV signatures fade.

Non-thermal velocities and temperatures evolve within the plasma sheet during the flare.

Abstract

In this multi-instrument paper, we search for evidence of sustained magnetic reconnection far beyond the impulsive phase of the X8.2-class solar flare on 2017 September 10. Using Hinode/EIS, CoMP, SDO/AIA, K-Cor, Hinode/XRT, RHESSI, and IRIS, we study the late-stage evolution of the flare dynamics and topology, comparing signatures of reconnection with those expected from the standard solar flare model. Examining previously unpublished EIS data, we present the evolution of non-thermal velocity and temperature within the famous plasma sheet structure, for the first four hours of the flare's duration. On even longer time scales, we use Differential Emission Measures and polarization data to study the longevity of the flare's plasma sheet and cusp structure, discovering that the plasma sheet is still visible in CoMP linear polarization observations on 2017 September 11, long after its last appearance in EUV. We deduce that magnetic reconnection of some form is still ongoing at this time - 27 hours after flare onset.