Hard X-Ray Source Motions in the 2002 July 23 Gamma-Ray Flare

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is used to study the hard X-ray (HXR) source motions of the 2002 July 23 γ-ray flare. Above 30 keV, at least three HXR sources are observed during the impulsive phase that can be identified with footpoints of coronal magnetic loops that form an arcade. On the northern ribbon of this arcade, a source is seen that moves systematically along the ribbon for more than 10 minutes. On the other ribbon, at least two sources are seen that do not seem to move systematically for more than half a minute, with different sources dominating at different times. The northern source motions are fast during times of strong HXR flux but almost absent during periods with low HXR emission. This is consistent with magnetic reconnection if a higher rate of reconnection of field lines (resulting in a higher footpoint speed) produces more energetic electrons per unit time and therefore more HXR emission. The absence of footpoint motion in one ribbon is inconsistent with simple reconnection models but can be explained if the magnetic configuration there is more complex.