Eruption of the magnetic flux rope in a fast decayed active region

Abstract

An isolated and fast decayed active region (NOAA 9729) was observed when passing through solar disk. There is only one CME related with it that give us a good opportunity to investigate the whole process of the CME. Filament in this active region rises up rapidly and then hesitates and disintegrates into flare loops. The rising filament from EIT images separates into two parts just before eruption. A new filament reforms several hours later after CME and the axis of this new one rotates clockwise about 22 degrees comparing with that of the former one. We also observed a bright transient J-shaped X-ray sigmoid immediately appears after filament eruption. It quickly develops into a soft X-ray cusp and rises up firstly then drops down. Two magnetic cancelation regions have been observed clearly just before filament eruption. Moreover, the magnetic flux rope erupted as the magnetic helicity approach the maximum and the normalized helicity is -0.036 when the magnetic flux rope erupted, which is close to the prediction value based on the theoretical non-linear force-free model.