Quasi-Periodicity in the Parsec-Scale Jet of the Quasar 3C 345

Abstract

We have observed the Quasar 3C345 with VSOP and the VLBA at four different frequencies (1.6GHz, 5GHz, 22GHz and 43GHz), making a total of 24 epochs, from 1997.40 to 1999.69. This study, combined with previous observations, reveals an about 9 year period in the parsec-scale jet. This periodicity can be found in the initial position angles, the trajectories and the flux density evolution of the jet components. A binary black hole model with an orbital period of 8.5 years (observer frame) can be successfully applied to our results. The 125 year superimposed precession period of the accretion disc would explain the observed drift in the initial component position angles.