Non-thermal processes associated with rising structures and waves during a "halo" type CME

Abstract

We analyse structures and events connected with a flare-associated "halo" type coronal mass ejection (CME) observed on December 18, 2000. A GOES C7.0 class X-ray flare started at 11:02 UT in NOAA Active Region 9269, located at N14 E03. Yohkoh SXT observed slowly rising soft X-ray loops already some 5 min before flare start. Ha images show a two-ribbon flare, remote brightenings, and a partly disappearing filament near the active region. A metric radio precursor was observed to start at 11:06:30 UT, simultaneously with impulsive emission in hard X-rays and microwaves. The frequency-drifting precursor envelope was superposed with J- and reverse drift bursts. The radio bursts traced large-scale soft X-ray loop structures about 160000 km away from the flare core, and hard X-ray emission was observed at the ends of some of these loops. The precursor emission points to a rising structure where electron acceleration takes place. Later on, a radio type II burst (signature of a propagating shock, driven either by an ejecta or a blast wave) and an EIT wave were observed. We conclude that possible sources for the rising structure and accelerator of electron beams are (1) large-scale loops that connect the flare core region and the precursor site in the close vicinity of two separate rising filaments, and (2) a growing shock that accelerates electrons along closed field lines until the multipolar field is opened and the CME is lifted off. As neither X-ray nor EUV ejecta could be observed whether in the direction of the type II burst or near the radio precursor, we find some support for the shock wave scenario. © ESO 2005.