Failed filament eruption inside a coronal mass ejection in active region 11121

Aims. We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast<br/>limb on November 6, 2010.<br/>Methods. We used a time series of SDO/AIA 304, 171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as ROSA<br/>and ISOON Hα images to study the erupting active region.<br/>Results. We identify coronal loop arcades associated with a quadrupolar magnetic configuration, and show that the expansion and<br/>cancellation of the central loop arcade system over the filament is followed by the eruption of the filament. The erupting filament<br/>reveals a clear helical twist and develops the same sign of writhe in the form of inverse γ-shape.<br/>Conclusions. The observations support the “magnetic breakout” process in which the eruption is triggered by quadrupolar reconnection<br/>in the corona. We propose that the formation mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic helical<br/>kink instability. The eruption has failed because of the large-scale, closed, overlying magnetic loop arcade that encloses the active<br/>region