Large-Amplitude Oscillation of an Erupting Filament as Seen in EUV, H-alpha and Microwave Observations

We present multiwavelength observations of a large-amplitude oscillation of a polar crown filament on 15 October 2002. The oscillation occurred during the slow rise (about 1 km/s) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope onboard SOHO. The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The period of oscillation was about two hours and did not change significantly during the oscillation. We also identified the oscillation as a "winking filament" in the H-alpha images taken by the Flare Monitoring Telescope, and as a spatial displacement in 17 GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated.