Flux densities in R band (a) and at 15 GHz (b) and behaviour in time of viewing angle (c) of optical-emitting region (red) and radio-emitting region (blue). The red and blue lines in panels a and b show cubic spline interpolations on the binned optical and radio data, respectively. They represent the long-term trends of the flux. Deboosted optical flux densities are displayed in orange; they represent fluxes corrected for the effect of variable Doppler beaming. In the bottom panels, the yellow areas highlight the periods where the optical-emitting region is better aligned with the line of sight than the radio zone, and hence the optical radiation is more beamed than the radio emission.