γ-ray light curve (a), flux densities in R band (b), and behaviour in time of viewing angle (c) of the γ-ray emitting region (black) and of the optical emitting region (red). The black and cyan lines in panel a represent the original and rescaled (see Sect. 9) cubic spline interpolations on the binned γ-ray data, respectively; the red line in panel b shows the cubic spline interpolation on the binned optical data. In the bottom panel, the yellow areas highlight the periods where the optical emitting region is better aligned with the line of sight than the γ-ray zone, and hence the optical radiation is more beamed than the γ-ray emission.