Soft X-ray Imaging of Impulsive Evaporation
Abstract
The time development of a solar flare can often be broken into two phases, viz. the impulsive phase and the gradual phase. For many reasons the impulsive phase is known to result from powerful electron acceleration, to energies of tens of keV (and higher), with a total energy that is a large fraction of the energy subsequently radiated in various flare emissions. A grazing-incidence soft X-ray telescopes on board the Yohkoh spacecraft now enables us to study the few-keV properties of the impulsive phase for the first time. In a representative set of impulsive solar flares, we find an excellent match between the soft X-ray time profiles at the footpoints of coronal magnetic flux tubes and the hard X-ray impulsive emission. The hard X-ray images directly show the sites of the particle precipitation. The impulsive soft X-ray emission could arise directly as non-thermal bremsstrahlung, extending to the few-keV range; or it could contain contributions from the impulsively evaporating plasma seen during the process of the flare explosion from the chromosphere. We discuss these interpretations and the physics resulting from them.
- Publication:
-
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1992
- Bibcode:
- 1992AAS...181.5501H