Using RHESSI data, we have analyzed some 172 hard X-ray peaks during 53 solarflares which exhibited a double-footpoint structure. Fitting both footpointswith power-laws, we find that spectral index differences range mostly between 0to 0.6, and only rarely go beyond. Asymmetries between footpoints were notobserved to be significantly dependent on their mean heliographic position,their relative position with respect to each other, nor their orientation withrespect to the solar equator. Assuming a symmetric acceleration process, it isalso clear that differences in footpoint spectral indices and footpoint fluxratios can seldom be attributed to a difference in column densities between thetwo legs of a coronal loop. Our results corroborate better the magnetic mirrortrap scenario. Moreover, footpoint asymmetries are more marked during times ofpeak HXR flux than when averaging over the whole HXR burst, suggesting that themagnetic configuration evolves during individual HXR bursts. We observed also alinear correlation between the peak 50-keV flux and the peak GOES 1-8A channelflux, and that HXR burst duration seem correlated with loop length.
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