Observations of simultaneous coronal loop shrinkage and expansion during the decay phase of a solar flare

¹ Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland, UK e-mail: jkhan@spd.aas.org
² Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA 94304, USA

Received: 29 November 2005
Accepted: 9 March 2006

Abstract

We report what we believe are the first direct and unambiguous observations of simultaneous coronal magnetic flux loop shrinkage and expansion during the decay phase of a solar flare. The retracting and expanding loops were observed nearly face-on (i.e., with the loop major axis approximately orthogonal to the line of sight) in emission in imaging data from the Yohkoh Soft X-ray Telescope (SXT). The retracting loop is observed to shrink with a speed of 118 ± 66 km s^-1. The faint outward moving loop-like feature occurred ~200´´ above the shrinking loop during the time of the shrinking loop. We estimate the speed of the outward moving loop was ~129 ± 74 km s^-1. We interpret the shrinking loop and simultaneous outward moving loop as direct evidence for reconnected magnetic field lines during a flare.