Problems and progress in flare fast particle diagnostics Original Research Article

Recent progress in the diagnosis of flare fast particles is critically discussed with the main emphasis on high resolution hard X-ray (HXR) data from RHESSI and coordinated data from other instruments. Spectacular new photon data findings are highlighted as are advances in theoretical aspects of their use as fast particle diagnostics, and some important comparisons made with interplanetary particle data. More specifically the following topics are addressed: (a) RHESSI data on HXR (electron) versus gamma-ray line (ion) source locations. (b) RHESSI hard X-ray source spatial structure in relation to theoretical models and loop density structure. (c) Energy budget of flare electrons and the Neupert effect. (d) Spectral deconvolution methods including blind target testing and results for RHESSI HXR spectra, including the reality and implications of dips inferred in electron spectra. (e) The relation between flare in situ and interplanetary particle data.