Observational Study of Solar X-ray Plasma Ejections

X-ray plasma ejections (XPEs) often occurred around the impulsive phase of solar flares and have been well observed by the SXT aboard Yohkoh. In this study we have carried out observational studies of XPEs in order to address the identification of the XPE. Firstly, we have made a comprehensive statistical study of the relationship between XPEs and coronal mass ejections (CMEs). For this we considered 279 limb flares from all flare mode data in Yohkoh SXT observation during the last solar maximum (1999-2001). For these flares, we examined associated XPEs and CMEs to make clear the relationship between XPEs and CMEs temporally and spatially. Secondly, we have classified 137 XPEs into five groups according to their shape, such as loop-type (60 events), spray-type (40 events), jet-type (11 events), confined ejection (18 events), and others (8 events). We also examined the physical properties for each group. Thirdly, we have investigated the kinematic properties of the XPEs. For this purpose, we examined the speed profiles of selected events and estimated the representative speeds of 137 XPEs to compare with the CME speeds and the estimated Alfven speeds. Main results of our study are summarized as follows: (1) the XPE usually does not represent the early signatures of the CME leading edge but are closely associated with CMEs; (2) the group-dependence of XPE properties, such as CME association and speed, imply that the physical characteristics of the XPEs are closely associated with magnetic field configurations near the reconnection regions; (3) the majority of XPEs are not likely to be the X-ray counterpart of CMEs but outflows generated by magnetic reconnection, at least from its kinematical point of view.