Observation of a Solar Flare at the Limb with the Yohkoh Soft X-Ray Telescope

A long-enduring soft X-ray flare at the solar limb was well observed by the Soft X-ray Telescope aboard the Yohkoh spacecraft from its pre-flare stage through the post-flare phase. A “helmet streamer” arch appears several hours prior to the flare, in association with a continuous expansion and restructuring of the active-region magnetic structure. This arch then starts to flare, and increases its height and footpoint separation at v = 10–30 km s−1. The arch has a complex temperature structure in the rising phase, whereas the outer arches have systematically higher temperatures in the decay phase. Magnetic reconnection in a neutral sheet at the loop top, created by pre-flare magnetic restructuring, would explain this type of flare.