34th Solar Physics Division Meeting, June 2003
Session 14 RHESSI Results I
Oral, Wednesday, June 18, 2003, 9:00am-12:00noon, Auditorium

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[14.06] Hard X-ray Sources and Motions in the July 23, 2002 Gamma-Ray Flare

Sam Krucker, G. H. Hurford, R. P. Lin (Space Sciences Lab, University of California, Berkeley)

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is used to study the Hard X-ray (HXR) emission of the July 23, 2002 gamma-ray flare. In the inital rise (00:21-00:26~UT), a probably non-thermal coronal HXR source dominates with weaker emission from foopoints in two ribbons visible in H-alpha and EUV. During the main impulsive phase (00:27-00:42~UT), HXR footpoint emission dominates above 30 keV, whereas at lower energies a gradual coronal HXR source is seen. The footpoint emission originates from several sources close to a magnetic neutral line. The time profiles of two footpoints apparently in opposite polarity regions are similar, suggesting magnetic connection between them. The relative separation of these two footpoints increases in time. On the positive polarity side, a source moves roughly parallel to the neutral line with a speed of up to ~100 km s-1; on the negative polarity side with slightly weaker magnetic fluxes, several sources are seen that do not seem to move systematically, with different sources dominating at different times. The coronal source shows an elongated structure, possibly containing more than one source, that moves with a similar speed in almost the same direction as the moving footpoint. The speed of both the footpoint and the coronal source motions are roughly correlated with the total HXR flux of the footpoints. The source motions are fast during times of strong HXR flux, but almost absent during periods with low HXR emission. These observations are consistent with magnetic reconnection models in which a higher rate of reconnection of field lines produces more energetic electrons per unit time and therefore more HXR emission, and also results in a higher apparent speed of the HXR sources at the footpoints of newly reconnected loops.


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Bulletin of the American Astronomical Society, 35 #3
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