Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows

TL;DR

This study analyzes an M7.7 solar flare, revealing that particle acceleration and plasma heating primarily occur in reconnection outflows, with observations of plasmoid ejections, loop contractions, and double coronal X-ray sources providing new insights into magnetic reconnection processes.

Contribution

It provides new observational evidence that particle acceleration and heating happen in reconnection outflows rather than at the reconnection site itself, advancing understanding of solar flare energetics.

Findings

Reconnection outflows include plasmoid ejections and contracting loops at speeds up to 1050 km/s.

Double coronal X-ray sources are spatially separated and their centroid separation decreases with energy.

The highest plasma temperature is located near the nonthermal X-ray loop-top source, below the original cusp heights.

Abstract

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially separated double coronal X-ray sources with centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descent, which we ascribe to the interplay among multiple processes including the upward development of reconnection and the downward contractions of reconnected loops. The impulsive phase onset is delayed by 10 minutes from the start of the descent, but coincides with the rapid speed increases of the upward plasmoids, the individual loop shrinkages, and the overall loop-top descent, suggestive of an intimate relation of the energy release rate and reconnection outflow speed.