Desynchronization between CME Acceleration and Flare Reconnection

Abstract According to the standard coronal mass ejection (CME) model, both the flare and the CME are a result of the common process of magnetic reconnection. This implies that the CME impulsive acceleration and the flare reconnection should correlate in time. However, observations suggest that this correlation may break for CMEs associated with weak flares. In this work, we aim to find experimental evidence of such desynchronization. For this study, we chose a CME that 1) was associated with a weak B7.1 flare; 2) was continuously tracked from the solar surface up to the outer corona with high-cadence observations; 3) for which X-ray images were available. We measured the CME acceleration profile and compared it with the reconnection signatures: the derivative of the soft X-ray (SXR) emission and the motion of flare ribbons. The studied CME had non-trivial kinematics. It first impulsively accelerated to 440 km s-1 over 20 min, then decelerated to 280 km s-1 over 15 min, and then slowly accelerated up to 660 km s-1 over 2 h. We observed reconnection signatures only during the deceleration and second acceleration phases, suggesting that the main impulsive acceleration occurred without flare reconnection. We interpreted the first acceleration phase as a consequence of the kink instability. As the flux rope rose, it stretched the current sheet below it, which slowed down the CME. Eventually, the reconnection started inside the newly formed current sheet, and the CME started to accelerate again. These results show that CMEs can accelerate significantly without magnetic reconnection and exhibit a complex acceleration structure. This means that different mechanisms play a role in CME acceleration at different stages of its evolution.