Analysis of the color variability of BL Lac in the visible range during the 1997 outburst

The color variability of BL Lac during the strong 1997 outburst was studied. It was found that the energy distribution in the spectrum of the variable source, which determines the object’s photometric behavior, did not vary during the outburst. It was a power- law spectrum and was flatter than during other, lower-power out-bursts. There is no doubt of the synchrotron nature of the variable source.