Eruption of an active-region filament driven by an emerging bipole

A section of an S-shaped filament underwent an eruption in a sigmoidal active region (AR 8027) with S-shaped coronal structure, which was clearly driven by a bipole emerging below the NW end of the filament. The bipole with two separating poles showed typical characteristics of emerging flux region (EFR) and its axis rotated counterclockwise. Two cancelling magnetic features (CMFs) were formed between the two poles and adjacent flux with opposite polarity and substantial flux cancellation occurred in them. Along with the bipole emergence the filament was strongly disturbed. Just before the filament eruption, two X-ray loops overlying the filament brightened, an axial X-ray structure and then a cusp structure appeared. During the eruption first the whole filament rose and then its SE end broke away from the chromosphere, while its NW end remained stationary. Helical structure and motion were observed in the filament body and downward mass motion in the two ends. After the eruption, a major part of the filament remained and slowly returned to quiescence, and an X-ray arcade and an axial structure formed. These observations suggest that the eruption resulted from the interaction between the bipole and the overlying loops. We provide evidence that steady photospheric reconnection between their footprints took place in the two CMFs during the bipole emergence.