Soft-hard-soft spectral behaviorobserved by RHESSI and HXRS

Hugh Hudson

Frantisek Farnik

ESPM-10 meetingPrague, Sept. 11, 2002

Coronal structure and flare hard X-rays

Fletcher et al., 2001Cargill & Priest, 1995

http://isass1.solar.isas.ac.jp/~hudson/cartoons

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)

Benz, 1977

An early example of SHS

A nice example from HXRS

Sep. 24, 2001Farnik et al., 2002

RHESSI vs HXRS29-43 keV

QuickTime™ and aYUV420 codec decompressorare needed to see this picture.

Theory and SHS

• Benz (1977) notes consistency of SHS relationship with a stochastic acceleration process (Fx ~ -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 Fx (posters)

• In general, theorists of flare particle acceleration should start with SHS; it is a fundamental morphology of the impulsive phase

Jakimiec et al. 1998

10 min

Soft-hard-harder etc. pattern

Cliver et al., 1986

SHS at energies above the “knee”

Fletcher & Hudson 2002

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