γ-ray fluxes at 1 GeV versus optical fluxes in R band. Each data point of γ-ray light curve has been paired with the average of the optical points acquired within 6 h. Solid lines represent linear regressions to the whole dataset (black), to the data points with optical log(ν F_ν) less than −9.3 (red), and to the data points with optical log(ν F_ν) greater than −9.3 (blue). The green line represents a cubic regression.