Breakout Reconnection and Eruption in a Double Null-point Topology

The breakout model explains a wide range of solar eruptions from small-scale jets to large-scale CMEs. However, it remains unclear why some eruptions are successful while others remain confined. Using SDO/AIA, STEREO, and RHESSI observations, we analyzed an eruption associated with a three-ribbon flare that occurred in a null-point topology (fan-spine configuration) within Active Region NOAA 11791. This AR is embedded within a large pseudostreamer between two coronal holes. About 4 hours prior, we detected evidence of interchange reconnection at the 3D null that produced a faint jet and a B-class flare without any filament eruption. Continued flare reconnection below the filament built a flux rope that rose slowly and later generated the two-ribbon C1.4 flare. The flux rope interacted with the deformed null at the top of the fan, producing a remote (third) ribbon at the base of the separatrix along with the ejection of the flux rope. For the first time, we detected a remote soft and hard X-ray source (3-25 keV) associated with the third ribbon in RHESSI images during the explosive breakout reconnection phase. Weak, narrow, coronal (25-180 MHz) and interplanetary (0.1-10 MHz) Type-III radio bursts were also detected during this phase, suggesting that electron beams from the null were ejected through the outer corona into the heliosphere. In addition, we observed multiple plasmoids in two places: above the rising flux rope, most likely formed in the breakout current sheet (the deformed null), and in a vertical flare current sheet below the flux rope, most likely due to quasiperiodic flare reconnection. The flux rope ejected from the inner system encountered the overlying arcade and 3D null of the big pseudostreamer higher in the corona, preventing the escape of the flux rope and the formation of a significant coronal mass ejection. However, coronagraph images revealed a faint loop-like structure arising from the pseudostreamer that propagated laterally southward with ~270 km s^-1. We suggest that the main factors leading to the confined filament eruption are (i) lack of significant breakout reconnection between the rising flux rope and the overlying arcade due to an unfavorable relative orientation of these flux systems; and/or (ii) insufficient free energy of the flux rope to overcome the tension forces of the overlying arcades.