Investigating Energetic X-Shaped Flares on the Outskirts of A Solar Active Region

Abstract

Typical solar flares display two quasi-parallel, bright ribbons on the chromosphere. In between is the polarity inversion line (PIL) separating concentrated magnetic fluxes of opposite polarity in active regions (ARs). Intriguingly a series of flares exhibiting X-shaped ribbons occurred at the similar location on the outskirts of NOAA AR 11967, where magnetic fluxes were scattered, yet three of them were alarmingly energetic. The X shape, whose center coincided with hard X-ray emission, was similar in UV/EUV, which cannot be accommodated in the standard flare model. Mapping out magnetic connectivities in potential fields, we found that the X morphology was dictated by the intersection of two quasi-separatrix layers, i.e., a hyperbolic flux tube (HFT), within which a separator connecting a double null was embedded. This topology was not purely local but regulated by fluxes and flows over the whole AR. The nonlinear force-free field model suggested the formation of a current layer at the HFT, where the current dissipation can be mapped to the X-shaped ribbons via field-aligned heat conduction. These results highlight the critical role of HFTs in 3D magnetic reconnection and have important implications for astrophysical and laboratory plasmas.

accepted for publication in Scientific Reports

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Cited by in corpus (7)

• Flare-productive active regions
• Critical Height of the Torus Instability in Two-Ribbon Solar Flares
• Witnessing a Large-scale Slipping Magnetic Reconnection along a Dimming Channel during a Solar Flare
• Reconstruction of a Large-scale Pre-flare Coronal Current Sheet Associated with an Homologous X-shaped Flare
• Non-potential field formation in the X-shaped quadrupole magnetic field configuration
• Untwisting Jets Related to Magnetic Flux Cancellation
• A Magnetic Bald-Patch Flare in Solar Active Region 11117