VLBI observations have shown that the parsec-jet of 3C 345 is formed by several components , ejected from the core with superluminal velocities and travelling along bent trajectories on the plane of the sky .
We interpret the differences in velocity and position angle among the different features at formation time as the result of parsec-scale precession of the relativistic jet and calculate the aperture angle of the precession cone , the angle between the cone axis and the line of sight and the Lorentz factor associated with the jet bulk motion .
We assumed a precession period of 10.1 yr , which is one of the B -band light curve long-term periods reported in the literature .
We propose that boosting of the underlying jet emission , which is time-dependent due to precession , is responsible for this long-term optical variability .
Jet precession with periods of several years can be produced in super-massive black hole binary systems , when the secondary black hole is in an orbit non-coplanar with the primary accretion disk , inducing torques in the inner parts of the disk .
Assuming that this mechanism is responsible for the jet precession in 3C 345 , we estimate upper and lower limits for the masses of the two black holes , as well as their mean separation .
We found a correlation between the formation of jet components and the occurrence of strong optical flares , as well as a very strong anti-correlation between the intensity of these flares and the time required for the components to reach the maximum flux density at radio frequencies .