The CME-flare relationship: Are there really two types of CMEs?

Abstract

We present a statistical analysis of 545 flare-associated CMEs and 104 non-flare CMEs observed in the heliocentric distance range 2–30 solar radii. We found that both data sets show quite similar characteristics, contradicting the concept of two distinct (flare/non-flare) types of CMEs. In both samples there is a significant fraction of CMEs showing a considerable acceleration or deceleration and both samples include a comparable ratio of fast and slow CMEs. We present kinematical curves of several fast non-flare CMEs moving at a constant speed or decelerating, i.e., behaving as expected for flare-associated CMEs. Analogously, we identified several slow flare-CMEs showing the acceleration peak beyond a height of 3 solar radii. On the other hand, it is true that CMEs associated with major flares are on average faster and broader than non-flare CMEs and small-flare CMEs. There is a well-defined correlation between the CME speed and the importance of the associated flare. In this respect, the non-flare CMEs show characteristics similar to CMEs associated with flares of soft X-ray class B and C, which is indicative of a “continuum” of events rather than supporting the existence of two distinct CME classes. Furthermore, we inferred that CMEs whose source region cannot be identified with either flares or eruptive prominences are on average slowest. The results indicate that the magnetic reconnection taking place in the current sheet beneath the CME significantly influences the CME dynamics.