Deconstructing blazars: A different scheme for jet kinematics in flat-spectrum AGN

Abstract

Recent VLBI studies of the morphology and kinematics of individual BL Lac objects (S5 1803+784, PKS 0735+178, etc.) have revealed a new paradigm for the pc-scale jet kinematics of these sources. Unlike the apparent superluminal outward motions usually observed in blazars, most, if not all, jet components in these sources appear to be stationary with respect to the core, while exhibiting strong changes in their position angles. As a result, the jet ridge lines of these sources evolve substantially, at times forming a wide channel-flow. We investigate the Caltech-Jodrell Bank flat-spectrum (CJF) sample of radio-loud active galaxies to study this new kinematic scenario for flat-spectrum AGN. We develop a number of tools that extract information about the apparent linear and angular evolution of the CJF jet ridge lines, as well as their morphology. In this way, we study both radial and non-radial apparent motions in the CJF jets. We find that approximately half of the sample shows appreciable apparent jet widths ($>10degrees$), with BL Lac jet ridge lines showing significantly larger apparent widths than both quasars and radio galaxies. In addition, BL Lac jet ridge lines are found to change their apparent width more strongly. Finally, BL Lac jet ridge lines show the least apparent linear evolution, which translates to the smallest apparent expansion speeds for their components. We find compelling evidence supporting a substantially different kinematic scenario for flat-spectrum radio-AGN jets and in particular for BL Lac objects. In addition, we find that variability is closely related to the properties of a source's jet ridge line. Variable quasars are found to show "BL Lac like" behavior, compared to their non-variable counterparts.

16 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (9)

• Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113
• A spinning supermassive black hole binary model consistent with VLBI observations of the S5 1928+738 jet
• The Simultaneous Low State Spectral Energy Distribution of 1ES 2344+514 from Radio to Very High Energies
• Infrared properties of blazars: putting the GASP-WEBT sources into context
• Periodic Gamma-ray Modulation of the blazar PG 1553+113 Confirmed by Fermi-LAT and Multi-wavelength Observations
• Flaring radio lanterns along the ridge line: long-term oscillatory motion in the jet of S5 1803+784
• Correlations between the peak flux density and the position angle of inner-jet in three blazars
• X-Ray Spectral Variability of the TeV HBL Blazar PG 1553+113 with XMM-Newton
• The Application of Ridgelines in Extended Radio Source Cross-Identification