Generation Mechanisms of Quasi-parallel and Quasi-circular Flare Ribbons in a Confined Flare

Abstract

We analyze a confined multiple-ribbon M2.1 flare (SOL2015-01-29T11:42) that originated from a fan-spine coronal magnetic field configuration, within active region NOAA 12268. The observed ribbons form in two steps. First, two primary ribbons form at the main flare site, followed by the formation of secondary ribbons at remote locations. We observe a number of plasma flows at extreme-ultraviolet temperatures during the early phase of the flare (as early as 15 min before the onset) propagating towards the formation site of the secondary ribbons. The secondary ribbon formation is co-temporal with the arrival of the pre-flare generated plasma flows. The primary ribbons are co-spatial with RHESSI hard X-ray sources, whereas no enhanced X-ray emission is detected at the secondary ribbons sites. The (E)UV emission, associated with the secondary ribbons, peaks ∼1 min after the last RHESSI hard X-ray enhancement. A nonlinear force-free model of the coronal magnetic field reveals that the secondary flare ribbons are not directly connected to the primary ribbons, but to regions nearby. Detailed analysis suggests that the secondary brightenings are produced due to dissipation of kinetic energy of the plasma flows (heating due to compression), and not due to non-thermal particles accelerated by magnetic reconnection, as is the case for the primary ribbons.

Transition from Circular-ribbon to Parallel-ribbon Flares Associated with a Bifurcated Magnetic Flux Rope

“…The emission characteristics at extreme ultraviolet wavebands were also different from that of flare F1. Some observations have already been described in Hernandez-Perez et al (2017). In contrast to flare F1, this flare has a much clearer remote ribbon (R4) in region W, and ribbon R2 in region M was not elongated.…”

“…Meanwhile, the plasma flowed to region W with a wider brightening region than in flare F1. Region E showed a similar phenomenon to region W instead of a successive brightening caused by region M. Hernandez-Perez et al (2017) interpreted such a phenomenon as magnetic reconnection in region M and plasma flow dissipation in regions E and W.…”

A Secondary Fan-spine Magnetic Structure in Active Region 11897

“…In a circular ribbon flare, the eruption of a filament or flux rope under the dome-shaped fan is often observed. As a result, two small quasi-parallel ribbons caused by the erupting filament would appear within the quasi-circular ribbon (Joshi et al 2015;Liu et al 2015;Zhang et al 2016b;Hernandez-Perez et al 2017;. This phenomenon suggests the simultaneous presence of at least two magnetic systems during this kind of flare: a magnetic flux rope (whose eruption causing the two small quasi-parallel ribbons) and a fan-spine topology (whose fan footprints in the lower atmosphere performing as a quasi-circular ribbon).…”

Development of a solar circular flare М6.4 according to observations in the Нα line

“…Âîíè âèíèêàþòü â àêòèâíèõ îáëàñòÿõ ç³ ñêëàäíèìè ìàãí³òíèìè êîí -ô³ãóðàö³ÿìè. Ñêëàäíà êîíô³ãóðàö³ÿ ìàãí³òíîãî ïîëÿ ³ òå, ùî ñïàëàõîâ³ ñòð³÷êè ìàëè êðóãëó ôîðìó, äîçâîëÿº ïðèïóñòèòè, ùî â àêòèâí³é îáëàñò³ NOAA 9087 ìàëà ì³ñöå ìàãí³òíà òîïîëîã³ÿ òèïó â³ÿëî-øèï (fan-spine), ùî ì³ñòèòü òðèâèì³ðíó íóëüîâó 3D-òî÷êó, â ÿê³é âñ³ òðè êîìïîíåíòè âåêòîðà ìàãí³òíîãî ïîëÿ äîð³âíþþòü íóëþ [15,32,39]. Íóëüîâ³ òî÷êè ìîaeóòü ñôîðìóâàòèñÿ â êîðîí³ ïðè âèõîä³ íîâîãî ìàã -í³òíîãî ïîòîêó [44].…”