Moving Plasmoid and Formation of the Neutral Sheet in a Solar Flare

Abstract

A spectacular erupting feature with a plasmoid-like structure is observed before and during the solar flare that occurred on the limb on 1991 December 2 with the Yohkoh soft X-ray telescope. The rise of a loop structure starts ~10 min before the flare, evolving to a plasmoid-like structure in the impulsive phase of the flare. The speed of the rising loop (plasmoid) is almost constant (~96 km s-1) throughout the observation. A clear X-shaped structure is formed underneath the rising plasmoid, and a bright soft X-ray loop is formed below the X-point. The X-shaped structure indicates a magnetic neutral point with a large-scale magnetic separatrix structure. Inverse-V-shaped high-temperature ridges are located above the soft X-ray loop and below the X-point. We interpret these as reconnected loops heated by slow shocks. A moving high-temperature (15 MK) source is found, coincident in position with the rising structure above the X-point. A hard X-ray source (33-53 keV) is located at the top of the soft X-ray flare loop. These two compact high-temperature sources located above and below the X-point would be formed by fast shocks due to the symmetric reconnection outflows both upward and downward from the X-point.