CME-Flare Association and the Role of Reconnection in CME Acceleration

The association of coronal mass ejections (CMEs) with flares is related to the question of whether reconnection is necessary for the CME eruption. Indeed, if reconnection happens during a CME eruption, the plasma is heated, which can be observed as a flare. In this work, we study the CME-flare association using data obtained with the Mg xii spectroheliograph on board the Complex Orbital Observations Near-Earth of Activity on the Sun (CORONAS-F) satellite. This instrument is sensitive only to the emission of plasma with a temperature greater than 4 MK, which makes it a convenient tool for detection of flaring activity. During our analysis, we first searched for CMEs detected during the Mg xii observations by the Large Angle and Spectroscopic Coronagraph (LASCO). Then, we visually checked the Mg xii images for flaring activity. We found that during the Mg xii observations (2001 – 2003), 198 CMEs were detected by LASCO. One hundred sixty of them (81%) are associated with flares seen in the Mg xii images. The strength of flares associated with narrow CMEs – jet-like ejecta – is uniformly distributed in the A – C GOES class range. The speed of narrow CMEs does not depend on the flare strength. For normal CMEs (motion of both magnetic field and plasma), the flare strength varies from A to X class with a peak of the distribution at the C level. The median speed and the kinetic energy of normal CMEs weakly depend on flare strength for weak flares (below C) and strongly for strong ones (M and X). Our results suggest that at solar maximum reconnection occurs during most CMEs. For strong flares (M and X), the reconnection is a dominant acceleration mechanism. For weak flares (C and below), other mechanisms start to play a bigger role.