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arXiv · 1509.08414

A Circular-ribbon Solar Flare Following an Asymmetric Filament Eruption

Chang Liu·Na Deng·Rui Liu·Jeongwoo Lee·Etienne Pariat·Thomas Wiegelmann·Yang Liu·Lucia Kleint·Haimin Wang
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Abstract

The dynamic properties of flare ribbons and the often associated filament eruptions can provide crucial information on the flaring coronal magnetic field. This Letter analyzes the GOES-class X1.0 flare on 2014 March 29 (SOL2014-03-29T17:48), in which we found an asymmetric eruption of a sigmoidal filament and an ensuing circular flare ribbon. Initially both EUV images and a preflare nonlinear force-free field model show that the filament is embedded in magnetic fields with a fan-spine-like structure. In the first phase, which is defined by a weak but still increasing X-ray emission, the western portion of the sigmoidal filament arches upward and then remains quasi-static for about five minutes. The western fan-like and the outer spine-like fields display an ascending motion, and several associated ribbons begin to brighten. Also found is a bright EUV flow that streams down along the eastern fan-like field. In the second phase that includes the main peak of hard X-ray (HXR) emission, the filament erupts, leaving behind two major HXR sources formed around its central dip portion and a circular ribbon brightened sequentially. The expanding western fan-like field interacts intensively with the outer spine-like field, as clearly seen in running difference EUV images. We discuss these observations in favor of a scenario where the asymmetric eruption of the sigmoidal filament is initiated due to an MHD instability and further facilitated by reconnection at a quasi-null in corona; the latter is in turn enhanced by the filament eruption and subsequently produces the circular flare ribbon.

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Chang Liu, Na Deng, Rui Liu, Jeongwoo Lee, Etienne Pariat, Thomas Wiegelmann, Yang Liu, Lucia Kleint, Haimin Wang. 2015-09-28. A Circular-ribbon Solar Flare Following an Asymmetric Filament Eruption. https://doi.org/10.1088/2041-8205%2F812%2F2%2Fl19

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