  Radio loud active galactic nuclei present a remarkable variety of signs
indicating the presence of periodical processes possibly originating in binary
systems of supermassive black holes, in which orbital motion and precession are
ultimately responsible for the observed broad-band emission variations, as well
as for the morphological and kinematic properties of the radio emission on
parsec scales. This scenario, applied to the quasar 3C345, explains the
observed variations of radio and optical emission from the quasar, and
reproduces the structural variations observed in the parsec-scale jet of this
object. The binary system in 3C345 is described by two equal-mass black holes
with masses of approximately 7*10^8 solar masses separated by ~0.33 pc and
orbiting with a period of ~480 yr. The orbital motion induces a precession of
the accretion disk around the primary black hole, with a period of ~2570 yr.
The jet plasma is described by a magnetized, relativistic electron-positron
beam propagating inside a wider and slower electron-proton jet. The combination
of Alfven wave perturbations of the beam, the orbital motion of the binary
system and the precession of the accretion disk reproduces the variability of
the optical flux and evolution of the radio structure in 3C345. The timescale
of quasi-periodic flaring activity in 3C345 is consistent with typical disk
instability timescales. The present model cannot rule out a small-mass orbiter
crossing the accretion disk and causing quasi-periodic flares.

Astrophysics