A study of flare-associated X-ray plasma ejections. I. Association with coronal mass ejections

We have made a comprehensive statistical study of the relationship between flare-associated X-ray plasma ejections and coronal mass ejections (CMEs). For this we considered all flare-mode data in Yohkoh SXT observations from 1999 April to 2001 March and then selected 279 limb flares seen at longitudes greater than 60 degrees. For these events, we identified whether there were associated X-ray plasma ejections or not. We found that about half (137/279) of the flares have X-ray plasma ejections, and we present a comprehensive list of these with their event times and speeds. We then determined whether there was an association between the flares with plasma ejections and CMEs detected by the Solar and Heliospheric Observatory LASCO instrument, on the basis of temporal and spatial proximity. It is found that about 69% (95/137) of the X-ray plasma ejections are associated with CMEs and that about 84% (119/142) of the events without plasma ejections do not have related CMEs. The associations are found to increase with flare strength and duration. We find that X-ray plasma ejections occur nearly simultaneously with the hard X-ray flare peak, supporting the idea that the X-ray plasma ejections are tightly associated with the flaring process. When the CMEs are extrapolated into the Yohkoh field of view for 43 selected, well-observed events, it is found that about 80% of the CMEs preceded X-ray plasma ejections, by approximately 20 minutes on average. Our results show that X-ray plasma ejections usually do not represent the early signature of a CME's leading edge but are closely associated with CMEs.