kernel would be detected. In this case, however, the random noise would increase as well and such cases would have to be studied case by case. Although it certainly is possible to go through our small sample case by case, we aim at a much larger set of flares for the future and then the manual intervention is not thinkable.

We also need to point out that we deal with the $f$ value as if it is an exact value. One has to keep in mind that there are two kinds of errors appearing in $f$: first it is the measurement error of magnetic induction and its propagation through calculation of the derivative, and second the projection error due to the violation of the plan-parallel approximation. The uncertainty of the first kind is suppressed by smoothing of the magnetic field induction prior to the calculation of the derivatives. The uncertainties are further lowered in a statistical sense, because at least 7000 points in the case of C1 flares enter the histogram, ten times more in case of CP, and millions in the other two cases. The bin-to-bin oscillations seen in Fig. \[fig:histograms\] give an idea about the noise levels.

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