Can we explain atypical solar flares?^⋆

¹ LESIA, Observatoire de Paris, LESIA, CNRS, UMPC, Univ. Paris Diderot, 5 place Jules Janseen, 92190 Meudon, France
e-mail: kevin.dalmasse@obspm.fr
² Department of Physics, DSB Campus, Kumaun University, Nainital- 263 002, India

Received: 6 December 2013
Accepted: 12 November 2014

Abstract

Context. We used multiwavelength high-resolution data from ARIES, THEMIS, and SDO instruments to analyze a non-standard, C3.3 class flare produced within the active region NOAA 11589 on 2012 October 16. Magnetic flux emergence and cancellation were continuously detected within the active region, the latter leading to the formation of two filaments.

Aims. Our aim is to identify the origins of the flare taking the complex dynamics of its close surroundings into account.

Methods. We analyzed the magnetic topology of the active region using a linear force-free field extrapolation to derive its 3D magnetic configuration and the location of quasi-separatrix layers (QSLs), which are preferred sites for flaring activity. Because the active region’s magnetic field was nonlinear force-free, we completed a parametric study using different linear force-free field extrapolations to demonstrate the robustness of the derived QSLs.

Results. The topological analysis shows that the active region presented a complex magnetic configuration comprising several QSLs. The considered data set suggests that an emerging flux episode played a key role in triggering the flare. The emerging flux probably activated the complex system of QSLs, leading to multiple coronal magnetic reconnections within the QSLs. This scenario accounts for the observed signatures: the two extended flare ribbons developed at locations matched by the photospheric footprints of the QSLs and were accompanied with flare loops that formed above the two filaments, which played no important role in the flare dynamics.

Conclusions. This is a typical example of a complex flare that can a priori show standard flare signatures that are nevertheless impossible to interpret with any standard model of eruptive or confined flare. We find that a topological analysis, however, permitted us to unveil the development of such complex sets of flare signatures.