X-ray plasma ejection associated with an impulsive flare on 1992 October 5: Physical conditions of X-ray plasma ejection

The 1992 October 5 flare was associated with an X-ray plasma ejection. Although the ejected plasma looks like a blob (or plasmoid) in short-exposure images, in long-exposure images it appears to be penetrated by or connected to the top of a large-scale loop. The ejecta had started to rise with a speed of similar to 250 km s(-1) before the main peak of the hard X-ray emission and was accelerated during the impulsive phase (to similar to 500 km s(-1)). We derived the physical parameters of the ejected plasma and obtained the following results: (1) The temperature of the ejected plasma was 10.6 +/- 3.6 MK. (2) Its density was (8-16) x 10(9) cm(-3) and was an order of magnitude larger than that of the typical active-region corona. (3) The mass of the ejected plasma was (2-4) x 10(13) g. (4) The kinetic energy of the ejecta was smaller than the thermal energy content of the flare loop. The overall features and evolution of the hot plasma ejection and flare are in rough agreement with those expected from the reconnection model, and the reconnection rate (M-A = V-in/V-A) is estimated to be similar to 0.02, where V-in is the speed of the inflow into the reconnection region, and V-A is the Alfven speed. Result 4, however, is not consistent with the assumption in some reconnection models that an ejected plasma stretches the overlying magnetic fields to form a current sheet and hence leads to magnetic reconnection. Instead, our results suggest that both X-ray plasma ejection and reconnection are a consequence of a common dynamical process such as the global MHD instability.