A Three-decade X-band VLBI Study of 3CR Lobe-dominated Quasar Nuclei

We report X-band VLBI observations of several 3CR lobe-dominated quasar nuclei from 1981 to 2010, mostly obtained with the NRAO VLBA. The goal is to follow flux density outbursts and to fully determine the jet morphology and kinematics on 1-100 pc scales. In 3C207, the core region has flux outbursts at mean intervals of ∼7 yr; one of these is actually a double outburst from a stationary true core and a swinging component ∼0.5 mas apart. The position angle (PA) of the swinging component varies by ∼40 , while the PA values of the jet components span ∼25 . The jet extends to ∼25 mas. Average superluminal speeds are ∼10c. One component shows apparent acceleration from 7c to 14c at 2-3 mas from the true core, in a jet recollimation zone that redirects the flow toward PA ∼90 . Individual jet components expand until reaching the recollimation zone. In 3C263 and other objects, some of the same phenomena are seen, including ejection of jet components over a range in PA, superluminal motion, and apparent acceleration, but to a lesser degree. Possible physical interpretations involving beaming, orientation, projection, precession, and magnetic effects are discussed.