The shortest time scales present in solar hard X-ray bursts

It is pointed out that isolated transient features in solar hard X-ray burst light curves, recently announced as having time scales of order 10 ms, have not yet been shown to be inconsistent with extreme statistical fluctuations in the Poisson counting noise. It is then shown that as far as persistent rapid time variations (white noise) are concerned, the available data do not demand the existence of any intrinsic solar time scales shorter than about 100 ms. This conclusion is supported by the fact that the high frequency power level of the Fourier transformed data approaches the Poisson noise expectation value above about 10 Hz and that the correlation of time scales calculated in widely separated energy channels deteriorates as the integration time used approaches 100 ms.