Magnetic Flux Ropes in Active Regions with M-Class Flares

Abstract

The dynamics of the magnetic field reconstructed in the nonlinear force-free approximation in the pre-flare and post-flare phases of M-class X-ray flares in seven active regions is considered: two flares with a coronal mass ejection (CME), two flares with eruption but no CMEs, and three flares without eruption. Extrapolation of the magnetic field to the corona of an active region (AR) showed that in all seven events at the site of the flare, 2–3 hours or less before it, a twisted state of the magnetic field is observed. It manifests itself in eruptive events most clearly in the form of magnetic ropes. Magnetic ropes and their dynamics are more pronounced in flares with CMEs; after the flare, they undergo a cardinal restructuring. In events with eruption, but without a CME, the flux ropes are pronounced, they are also rearranged after the flares, but the closed magnetic configuration prevents the coronal ejection. In events without eruption, flares occur in the interspot zone, where less pronounced flux ropes are observed, and in such events we do not observe significant changes in magnetic fields after the flare. In the pre-flare phase, at the location of the magnetic ropes, crossed loops are observed in all studied ARs in the extreme ultraviolet range; there is also a maximum brightness of microwave emission.