Rhessi observations of particle acceleration in solar flares Original Research Article

The NASA Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Small Explorer spacecraft was launched on 5 February 2002. Its primary objective is to investigate particle acceleration and energy release in solar flares through imaging spectroscopy of flare hard X-ray/gamma-ray continuum and gamma-ray lines emitted by energetic electrons and ions, respectively. Here we present preliminary results on the hard X-ray imaging spectroscopy of a flare, including the spatial variation with energy of the hard X-ray sources, the energy spectra and timing of the individual sources, and spectral features and total energy content. RHESSI observes continuous solar emission in the 3–10 keV energy range, with many microflares from many active regions. These microflares have a non-thermal power-law component similar to normal flares but with much steeper spectral slopes. We also present the first high-resolution gamma-ray line spectrum and the first imaging of gamma-ray lines, from the large X4.8 flare of 23 July 2002.