OBSERVATIONS AND MAGNETIC FIELD MODELING OF THE FLARE/CORONAL MASS EJECTION EVENT ON 2010 APRIL 8

We present a study of the flare/coronal mass ejection event that occurred in Active Region 11060 on 2010 April 8. This event also involves a filament eruption, EIT wave, and coronal dimming. Prior to the flare onset and filament eruption, both SDO/AIA and STEREO/EUVI observe a nearly horizontal filament ejection along the internal polarity inversion line, where flux cancellations frequently occur as observed by SDO/HMI. Using the flux-rope insertion method developed by van Ballegooijen, we construct a grid of magnetic field models using two magneto-frictional relaxation methods. We find that the poloidal flux is significantly reduced during the relaxation process, though one relaxation method preserves the poloidal flux better than the other. The best-fit pre-flare NLFFF model is constrained by matching the coronal loops observed by SDO/AIA and Hinode/XRT. We find that the axial flux in this model is very close to the threshold of instability. For the model that becomes unstable due to an increase of the axial flux, the reconnected field lines below the X-point closely match the observed highly sheared flare loops at the event onset. The footpoints of the erupting flux rope are located around the coronal dimming regions. Both observational and modeling results support the premise that this event may be initiated by catastrophic loss of equilibrium caused by an increase of the axial flux in the flux rope, which is driven by flux cancellations.