Figure 7: (a) Cross-correlation of the Swift-BAT gamma-ray (all energy channels) and TORTORA optical fluxes for the main (plateau) phase of the burst emission. (b) TORTORA optical flux shifted back 2 seconds along with correspondingly rebinned Swift-BAT gamma-ray flux. The correlation is with significance level of . Gamma-ray curve is arbitrarily scaled and shifted for illustrative purposes.