Heating and Eruption of a Solar Circular Ribbon Flare

TL;DR

This study analyzes the thermal evolution of a solar circular-ribbon flare, revealing early heating, magnetic reconnection processes, and the EUV late phase through DEM analysis and magnetic topology interpretation.

Contribution

It provides detailed DEM-based insights into the thermal dynamics and magnetic reconnection processes in a circular-ribbon flare, highlighting the role of null point reconnection.

Findings

Early temperature and emission measure rise before flare onset

Reconnection at the null point initiates prior to impulsive phase

Continued heating causes EUV late phase in flare loops

Abstract

We studied a circular-ribbon flare, SOL2014-12-17T04:51, with emphasis on its thermal evolution as determined by the Differential Emission Measure (DEM) inversion analysis of the extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO). Both temperature and emission measure start to rise much earlier than the flare, along with an eruption and formation of a hot halo over the fan structure. In the main flare phase, another set of ribbons forms inside the circular ribbon, and expands as expected for ribbons at the footpoints of a postflare arcade. An additional heating event further extends the decay phase, which is also characteristic of some eruptive flares. The basic magnetic configuration appears to be a fan-spine topology, rooted in a minority-polarity patch surrounded by majority-polarity flux. We suggest that reconnection at the null point begins well before the impulsive phase, when the null is distorted into a breakout current sheet, and that both flare and breakout reconnection are necessary in order to explain the subsequent local thermal evolution and the eruptive activities in this confined magnetic structure. Using local DEMs, we found a postflare temperature increase inside the fan surface, indicating that the so-called EUV late phase is due to continued heating in the flare loops.