Flux densities in the R band (a) and at 15 GHz (b) in 1993–2012, and behaviour in time of the viewing angle (c) of the optical emitting region (red) and of the 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. 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.