AAS 204th Meeting, June 2004
Session 47 When the Sun Went Wild
Topical Session, Tuesday, June 1, 2004, 2:30-4:00pm, 4:15-6:00pm, 702/704/706

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[47.15] Thermal and non-thermal energies of solar flares

P. Saint-Hilaire (Institute of Astronomy, ETHZ; Paul Scherrer Institut), A.O. Benz (Institute of Astronomy, ETHZ)

The energy of the thermal flare plasma and the kinetic energy of the non-thermal electrons in 9 medium-sized and 1 X-class solar flares have been determined from RHESSI observations. The emissions in the spectrum have been carefully separated. A reliable lower limit to the non-thermal energy, and the various errors of this estimate have been studied. The effects of albedo, non-uniform target ionization, hot target, and electron cross-section on the spectrum have been estimated. The turn-over or cut-off in the low-energy distribution of electrons remains the largest contribution to the error budget. About equally large are the errors of the thermal energy. They are due to the estimate of the flare volume, the assumption of the filling factor, and energy losses. Within a flare, the non-thermal/thermal ratio increases with accumulation time, as expected from loss of thermal energy due to radiative cooling or heat conduction. Our analysis suggests that the thermal and non-thermal energies are of the same magnitude. This surprising result may be interpreted by an efficient conversion of non-thermal energy to hot flare plasma or by additional energy input of high-energy ions, or by other flare energy input additional to the non-thermal electron channel.

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