The First Observation of a Rapidly Rotating Coronal Mass Ejection in the Middle Corona

Abstract

In this Letter, we present the first direct detection of a rotating coronal mass ejection (CME) in the middle corona (5-15 R _sun). The CME rotation rate is 60° day^-1, which is the highest rate reported yet. The Earth-directed event was observed by the STEREO/SECCHI and SOHO/LASCO instruments. We are able to derive the three-dimensional morphology and orientation of the CME flux rope by applying a forward-fitting model to simultaneous observations from three vantage points (SECCHI-A, -B, LASCO). Surprisingly, we find that even such rapidly rotating CME does not result in significant projection effects (variable angular width) in any single coronagraph view. This finding may explain the prevalent view of constant angular width for CMEs above 5 R _sun and the lack of detections of rotating CMEs in the past. Finally, the CME is a "stealth" CME with very weak low corona signatures as viewed from Earth. It originated from a quiet-Sun neutral line. We tentatively attribute the fast rotation to a possible disconnection of one of the CME footpoints early in the eruption. We discuss the implications of such rotations to space weather prediction.