1. Soft-hard-soft spectral behavior observed by RHESSI and HXRS Hugh Hudson Frantisek F a rnik ESPM-10 meeting Prague, Sept. 11, 2002

2. Coronal structure and flare hard X-rays Fletcher et al., 2001Cargill & Priest, 1995 http://isass1.solar.isas.ac.jp/~hudson/cartoons

3. Spectral signatures Neupert effect (Neupert, 1968) Soft-hard-soft spectral pattern (Parks & Winckler, 1971; Benz, 1975) Soft-hard-harder (?) spectral pattern (Cliver et al., 1986)

4. Benz, 1977 An early example of SHS

5. A nice example from HXRS Sep. 24, 2001 Farnik et al., 2002

6. RHESSI vs HXRS 29-43 keV

8. Theory and SHS Benz (1977) notes consistency of SHS relationship with a stochastic acceleration process (F x ~  -7/4 ) Accelerators requiring a separate trapping mechanism (e.g., Naito-Tsuneta) would be pushed to short time scales Direct acceleration in reconnection E-field (e.g., Litvinenko) does not yet predict a luminosity F x (posters) In general, theorists of flare particle acceleration should start with SHS; it is a fundamental morphology of the impulsive phase

9. Jakimiec et al. 1998

10. 10 min Soft-hard-harder etc. pattern Cliver et al., 1986

11. SHS at energies above the “knee” Fletcher & Hudson 2002

12. Conclusions Our experience with soft-hard-soft observed with scintillation counters (e.g., HXRS) has now been validated with RHESSI Non-thermal time scales are usually not determined by trapping; the spectral evolution is an intrinsic property of the acceleration mechanism The SHS pattern probably exists both above and below the spectral “knee” (which does exist) Deviations from SHS do occur and are most interesting