SPRG Seminars
February 17, 2009:
"Direct Observations of the Coronal Acceleration Region of a Solar Flare"
Säm Krucker, SSL
Solar flares essentially convert the intrinsic energy of coronal magnetic field into the kinetic energy of accelerated particles. Hard X-ray emission from flare-accelerated electrons produced by the bremsstrahlung mechanism provides the most direct diagnostics of electron acceleration. The most discussed coronal hard X-ray source has been the above-the-loop-top source observed in the Masuda flare. The poor spectral resolution of these observations, however, made an interpretation ambiguous, and the exact location of the acceleration remained elusive. We present high spatial and spectral resolution RHESSI hard X-ray observations of an above-the-loop-top source with simultaneous microwave observations from NoRH. These observations provide a unambiguous interpretation of above-the-loop-top sources: 1) The above-the-loop-top source itself is the acceleration region, where all electrons within an extended volume (1e27 cm3) are accelerated. 2) The distribution of the accelerated electrons is non-thermal, with a power law distribution extending from ~10 keV up to the relativistic range (few MeV). 3) The plasma beta in the acceleration region changes from the pre-flare value of ~0.01 to ~1, indicating that roughly half of the magnetic energy has been transformed into kinetic energy. [an error occurred while processing this directive]