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Astron. Astrophys. 356, 1067-1075 (2000)

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The fast and slow H[FORMULA] chromospheric responses to non-thermal particles produced during the 1991 March 13 hard X-ray/gamma-ray flare at ~ 08 UTC

G. Trottet 1, E. Rolli 2, A. Magun 3, C. Barat 4, A. Kuznetsov 5, R. Sunyaev 5 and O. Terekhov 5

1 DASOP, CNRS-UMR 8645, Observatoire de Paris, Section Meudon, 92195 Meudon, France
2 NUCATE/CRAAE, Unicamp, Rua Rôxo Moreira 1752, 13083-592 Campinas, SP, Brazil
3 University of Bern, IAP, Sidlerstrasse 5, 3012 Bern, Switzerland
4 Centre d'Etude Spatiale des Rayonnements, B.P. 4346, 31029 Toulouse, France
5 Space Science Institute, Profsoyuznaya 84/32, 117810 Moscow, Russia

Received 27 January 2000 / Accepted 18 February 2000


We present a multi-wavelength analysis of the X1.3/2B solar flare at 8 UTC on 1991 March 13 which includes H[FORMULA] images obtained by the fast digital H[FORMULA]-camera at Locarno-Monti at a rate of five images per second, full disk microwave measurements made with a time resolution of 0.1 s by the radiotelescopes in Bern and hard X-ray/gamma-ray data with a [FORMULA] 1 s time resolution by PHEBUS on board the GRANAT satellite. This set of multispectral data is used to investigate alternate forms of energy transport from the hot flare corona to the chromosphere. During this large flare, which exhibits two successive episodes of acceleration, energy transport took place within four loop systems of different sizes which expand with time and whose foot points were materialized by four H[FORMULA] kernels. It is shown that accelerated particles, most probably electrons, are the dominant form of energy transport, so that slower processes, such as conduction fronts, only play little role if any. Such a conlusion is demonstrated by the fact that the time evolution in intensity from the four observed kernels is well reproduced by a linear combination of the hard X-ray count rate and its time integral. Such a relationship, which is first established in this work, indicates that the H[FORMULA] response to non-thermal electrons consists of two components which evolve on different time scales, typically a few seconds and a few tens of seconds. The amplitude of the slow response is similar for the four kernels during the whole flare. In contrast, the amplitude of the fast response varies from one kernel to the other and is found to be the greater for the larger loop systems during the second and strongest episode of acceleration. Finally, during the first episode of acceleration, the fast H[FORMULA] response exhibits time variations with typical rise times of [FORMULA] 0.4-1.5 s which are nearly coincident with fast hard X-ray pulses of similar rise times. This is, so far, the most convincing evidence for correlated fast time structures in H[FORMULA] and hard X-rays. The ensemble of these results are discussed in the framework of models which simulate the chromospheric response of a loop atmosphere to heating by non-thermal electrons.

Key words: Sun: activity – Sun: chromosphere – Sun: flares – Sun: X-rays, gamma rays

Send offprint requests to: G. Trottet

© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000