2005 Lobanov & Roland 2005 Savolainen et al. 2007, 2012), while precession (sinusoidal variations) has been claimed in others (e.g., Stirling et al. Monotonic swings with no apparent periodicity ('wobbles') have been reported in some objects (e.g., Jorstad et al. The projected jet position angles can vary considerably (by up to 150° over a 12–16 yr time span Lister et al. In a number of blazars, the jets are observed (in projection) to undergo rapid swings of position angle in their innermost regions, but remain collimated on kiloparsec scales (for a review of several sources, see Agudo 2009). Most blazar jets feature 'knots' of emission that travel away from a (presumed stationary) 'core' at apparent speeds that range from ≲1 c to ≳50 c (e.g., Lister et al. Monitoring programs over at least a decade are able to (1) systematically characterize the long-term variability of the parsec-scale jet, including knot motions, jet wobbling, and precession (2) reveal the connection between multiwavelength outbursts and multimessenger events in the jet and (3) provide an observational basis for theoretical models of jet formation, acceleration, and collimation. The extraordinary resolution afforded by very long baseline interferometry (VLBI) enables detailed studies of the inner jets of AGNs on distance scales from 100 pc from the central supermassive black hole. 2016), exhibit the most extreme characteristics of all AGNs.

Blazars (Angel & Stockman 1980), with their jet directions oriented nearly along our line of sight (e.g., Lister et al. These physical effects cause the illusion of apparent superluminal motion, greatly enhanced flux densities, and reduced timescales of variability of flux and polarization (e.g., Blandford et al. The ultrarelativistic flow speeds of the jets of some active galactic nuclei (AGNs) strongly affect their observed characteristics through beaming, aberration, and light-travel delays. We find a connection between γ-ray states of blazars and their parsec-scale jet properties, with blazars with brighter 43 GHz cores typically reaching higher γ-ray maxima during flares. The fluctuations in position of the quasi-stationary components in radio galaxies tend to be parallel to the jet, while no directional preference is seen in the components of quasars and BL Lacertae objects. We investigate the variability of the position angle of each jet over the 10 yr of monitoring. We determine the typical values of these parameters for each jet and the average for each subclass of active galactic nuclei. We calculate the physical parameters of 273 knots with statistically significant motion, including their Doppler factors, Lorentz factors, and viewing angles. These accelerations occur mainly at locations coincident with quasi-stationary features. One-fifth of moving knots exhibit nonballistic motion, with acceleration along the jet within 5 pc of the core (projected) and deceleration farther out. Apparent speeds of these components range from 0.01 c to 78 c, and 18.6% of knots (other than the 'core') are quasi-stationary.

We implement a novel piecewise linear fitting method to derive the kinematics of 521 distinct emission knots from a total of 3705 total intensity images in 22 quasars, 13 BL Lacertae objects, and 3 radio galaxies. We analyze the parsec-scale jet kinematics from 2007 June to 2018 December of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array (VLBA) at 43 GHz under the VLBA-BU-BLAZAR program.

Parsec technologies logo vector