Xu, Y. Emslie, A.G., and Hurford, G.J., "RHESSI hard X-ray imaging spectroscopy of extended sources and the physical properties of acceleration regions in solar flares," ApJ 673, 576 (2008) ADS
Fleshing out the discovery by Veronig & Brown of "coronal thick target" hard X-ray sources, this paper does a rigorous model calculation on a sample of flaring loops. The basic idea is that electrons start out at a coronal point source and then collide, scatter, and radiate as they try to escape from their durance vile. Meanwhile, RHESSI has the energy resolution and imaging capability to watch this escape attempt in progress and to characterize it quantitatively.
One caveat would be that these are not common events; the authors selected ones for which they could do this analysis. Another would be that the forward-fit procedure used permits little flexibility in the modeling. One is in a sense building the answeer into the analysis.
9 March 2008