Evidence from the Extreme-Ultraviolet Imaging Spectrometer for Axial Filament Rotation before a Large Flare
Abstract
In this article, we present observations made with the Extreme-ultraviolet Imaging Spectrometer on-board the Hinode solar satellite, of an active region filament in the HeII emission line at 256.32Å. The host active region AR 10930 produces an X-class flare during these observations. We measure Doppler shifts with apparent velocities of up to 20km s-1, which are antisymmetric about the filament length and occur several minutes before the flare's impulsive phase. This is indicative of a rotation of the filament, which is in turn consistent with expansion of a twisted flux rope due to the MHD helical kink instability. This is the first time that such an observation has been possible in this transition-region line, and we note that the signature observed occurs before the first indications of pre-flare activity in the GOES solar soft X-ray flux, suggesting that the filament begins to destabilise in tandem with a reorganization of the local magnetic field. We suggest that this expansion is triggered by the decrease of magnetic tension around, and/or total pressure above, the filament.
- Publication:
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Publications of the Astronomical Society of Japan
- Pub Date:
- June 2009
- DOI:
- 10.1093/pasj/61.3.493
- Bibcode:
- 2009PASJ...61..493W
- Keywords:
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- Sun: activity;
- Sun: filaments;
- Sun: transition region