Coalescence of Macroscopic Magnetic Islands and Electron Acceleration from STEREO Observation

• Main Authors: Hong-Qiang Song (宋红强), Yao Chen (陈耀), Gang Li (李刚), Xiang-Liang Kong (孔祥良), Shi-Wei Feng (冯士伟)
• Format: Article
• Language: English
• Published: American Physical Society 2012-06-01
• Series: Physical Review X
• Online Access: http://doi.org/10.1103/PhysRevX.2.021015

Magnetic reconnection is a fundamental plasma process. Recent theoretical studies and numerical simulations have suggested that electrons can be efficiently accelerated in contracting magnetic islands and when magnetic islands coalesce. Using data from the STEREO spacecraft, we report in this article the first observation of macroscopic magnetic-island coalescence and a possible splitting, and the associated electron acceleration. On 24 May 2010, two magnetic islands were observed by both the STEREO-A and STEREO-B spacecraft to propagate out along the current sheet behind a coronal mass ejection (CME) and merge. Electron acceleration to above 10 keV is inferred through the observation of a type-III-like radio burst. The acceleration process occurred at a macroscopic scale, likely during the merging of the two magnetic islands. Our observation of the magnetic-island coalescence is supported by a 2.5-D axisymmetric magnetohydrodynamic simulation of CME in which the merging of post-CME magnetic islands is clearly identified.