PLASMOID EJECTIONS AND LOOP CONTRACTIONS IN AN ERUPTIVE M7.7 SOLAR FLARE: EVIDENCE OF PARTICLE ACCELERATION AND HEATING IN MAGNETIC RECONNECTION OUTFLOWS

Abstract

Where particle acceleration and plasma heating take place in relation to\nmagnetic reconnection is a fundamental question for solar flares. We report\nanalysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI.\nBi-directional outflows in forms of plasmoid ejections and contracting\ncusp-shaped loops originate between an erupting flux rope and underlying flare\nloops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are\nassociated with spatially separated double coronal X-ray sources with centroid\nseparation decreasing with energy. The highest temperature is located near the\nnonthermal X-ray loop-top source well below the original heights of contracting\ncusps near the inferred reconnection site. These observations suggest that the\nprimary loci of particle acceleration and plasma heating are in the\nreconnection outflow regions, rather than the reconnection site itself. In\naddition, there is an initial ascent of the X-ray and EUV loop-top source prior\nto its recently recognized descent, which we ascribe to the interplay among\nmultiple processes including the upward development of reconnection and the\ndownward contractions of reconnected loops. The impulsive phase onset is\ndelayed by 10 minutes from the start of the descent, but coincides with the\nrapid speed increases of the upward plasmoids, the individual loop shrinkages,\nand the overall loop-top descent, suggestive of an intimate relation of the\nenergy release rate and reconnection outflow speed.\n