The fast and slow H alpha chromospheric responses to non-thermal particlesproduced during the 1991 March 13 hard X-ray/gamma-ray flare at similar to08 UTC

We present a multi-wavelength analysis of the X1.3/-2B 'solar flare at 8 UT C on 1991 March 13 which includes Ha images obtained by the fast digital H alpha-camera at Locarno-Monti at a rate of five images per second, full dis k microwave measurements made with a time resolution of 0.1 a by the radiot elescopes in Bern and hard X-ray/gamma-ray data with a less than or equal t o 1 s time resolution by PHEBUS on board the GRANAT satellite. This set of multispectral data is used to investigate alternate forms of energy transpo rt from the hot flare corona to the chromosphere. During this large flare, which exhibits two successive episodes of acceleration, energy transport to ok place within four loop systems of different sizes which expand with time and whose foot points were materialized by four Her kernels. It is shown t hat accelerated particles, most probably electrons, are the dominant form o f energy transport, so that slower processes, such as conduction fronts, on ly play little role if any. Such a conlusion is demonstrated by the fact th at the time evolution in intensity from the four observed kernels is well r eproduced 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, in dicates that the Her response to non-thermal electrons consists of two comp onents 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 fas t response varies from one kernel to the other and is found to be the great er for the larger loop systems during the second and strongest episode of a cceleration. Finally, during the first episode of acceleration, the fast Hc t: response exhibits time variations with typical rise times of similar to 0.4-1.5 s which are nearly coincident with fast hard X-ray pulses of simila r rise times. This is, so far, the most convincing evidence for correlated fast time structures in Ha: and hard X-rays. The ensemble of these results are discussed in the framework of models which simulate the chromospheric r esponse of a loop atmosphere to heating by non-thermal electrons.