On the 2012 October 23 circular ribbon flare: emission features and magnetic topology

TL;DR

This study analyzes an X-class circular ribbon solar flare from 2012, revealing complex magnetic topology including a null-point, flux rope, and QSLs, and links emission features to magnetic reconnection processes.

Contribution

It provides a detailed magnetic topology analysis of a circular ribbon flare, integrating multi-wavelength observations with magnetic field extrapolation to explain emission features.

Findings

Identification of a 3D null-point, flux rope, and QSLs in the active region.

HXR sources located at flux rope footpoints indicating reconnection sites.

All three magnetic structures are essential to explain observed emission features.

Abstract

Circular ribbon flares are usually related to spine-fan type magnetic topology containing null-points. In this paper, we investigate an X-class circular ribbon flare on 2012 October 23, using the multi-wavelength data from the \textit{Solar Dynamics Observatory}, \textit{Hinode}, and the \textit{Ramaty High Energy Solar Spectroscopic Imager}. In \ion{Ca}{2} H emission, the flare showed three ribbons with two highly elongated ones inside and outside a quasi-circular one, respectively. A hot channel was displayed in the extreme ultraviolet (EUV) emissions that infers the existence of a magnetic flux rope. Two hard X-ray (HXR) sources in the 12--25 keV energy band were located at the footpoints of this hot channel. Using a nonlinear force-free magnetic field extrapolation, we identify three topological structures: (1) a 3D null-point, (2) a flux rope below the fan of the null-point, and (3) a large-scale quasi-separatrix layers (QSL) induced by the quadrupolar-like magnetic field of the active region. We find that the null-point is embedded within the large-scale QSL. In our case, all three identified topological structures must be considered to explain all the emission features associated with the observed flare. Besides, the HXR sources are regarded as the consequence of the reconnection within or near the border of the flux rope.