Subsecond time variations in solar flares around 100 keV: Diagnostics of electron acceleration

The present paper discusses the results of a systematic study of subsecond time variations performed on the PHEBUS observations of more than one hundred solar bursts detected around 100 keV. The analysis shows that: 1) a large percentage (73%) of hard X-ray bursts observed around 100 keV presents time features with rise times in the 100 ms-1 s range, 2) these time features are less systematically observed in long duration events, 3) there is a continuous distribution (during a single burst or for all the bursts of the sample) of the values of the different timescales derived from the analysis. The results are discussed with respect of the electron acceleration timescales in solar flares as well as in the context of the ``statistical flare'' scenario.