Large Magnetic Flux Rope Formation in an X2.1 Flare observed on September 6, 2011

TL;DR

This study combines observations and 3D MHD simulations to demonstrate that a large magnetic flux rope formed during the September 6, 2011, X2.1 solar flare, explaining associated flare ribbons and remote brightenings.

Contribution

The paper presents a data-constrained MHD simulation showing the formation of a large magnetic flux rope during a major solar flare, linking magnetic reconnection to observed flare features.

Findings

Formation of a large magnetic flux rope during the flare

Reconnection between sigmoidal and fan dome fields facilitated flux rope creation

Simulation footpoints match observed flare ribbons and brightenings

Abstract

Solar active region 11283 produced an X2.1 flare associated with a solar eruption on September 6, 2011. Observations revealed a preflare sigmoidal structure and a circular flare ribbon surrounding the typical two ribbon structure, along with remote brightenings located at a considerable distance from the main flare site. To interpret these observations in terms of the three dimensional (3D) coronal magnetic field dynamics, we conducted data constrained magnetohydrodynamic (MHD) simulations. Using a non linear force free field (NLFFF) as the initial condition, we reconstructed a realistic pre flare magnetic environment, capturing a sheared sigmoid above the polarity inversion line (PIL) surmounted by a fan spine structure. Our simulations revealed that reconnection between the sigmoidal field, the adjacent fan dome field lines, and the neighboring large loops facilitated the transfer of magnetic twist and led to the formation of a large magnetic flux rope (MFR). This transfer and propagation of twist are clearly visible throughout the MFR. As reconnection progresses, the entire fan spine structure expands along with the evolving MFR. A notable outcome of the simulation is that the footpoints of the newly formed MFR align closely with the observed circular flare ribbon and the remote brightening region. Our findings suggest that a large MFR formed during the X2.1 flare, providing a coherent explanation for the observed phenomena.