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Published October 2007 | public
Journal Article

Doppler boosting, superluminal motion, and the kinematics of AGN jets


We discuss results from a decade long program to study the fine-scale structure and the kinematics of relativistic AGN jets with the aim of better understanding the acceleration and collimation of the relativistic plasma forming AGN jets. From the observed distribution of brightness temperature, apparent velocity, flux density, time variability, and apparent luminosity, the intrinsic properties of the jets including Lorentz factor, luminosity, orientation, and brightness temperature are discussed. Special attention is given to the jet in M87, which has been studied over a wide range of wavelengths and which, due to its proximity, is observed with excellent spatial resolution. Most radio jets appear quite linear, but we also observe curved non-linear jets and non-radial motions. Sometimes, different features in a given jet appear to follow the same curved path but there is evidence for ballistic trajectories as well. The data are best fit with a distribution of Lorentz factors extending up to γ∼30 and intrinsic luminosity up to ~10^(26) W  Hz^(−1). In general, gamma-ray quasars may have somewhat larger Lorentz factors than non gamma-ray quasars. Initially the observed brightness temperature near the base of the jet extend up to ~5×10^(13) K which is well in excess of the inverse Compton limit and corresponds to a large excess of particle energy over magnetic energy. However, more typically, the observed brightness temperatures are ~2×10^(11) K, i.e., closer to equipartition.

Additional Information

© 2007 Springer Science+Business Media B.V. Received: 10 April 2007; Accepted: 31 July 2007; Published online: 1 September 2007. This paper is based on observations made with the Very Long Baseline Array which is a facility of the National Radio Astronomy Observatory which is operated by Associated Universities, Inc., under a cooperative agreement with the National Science Foundation. Part of this work was done by YYK, MLL and DCH during their Karl Jansky postdoctoral fellowship at the National Radio Astronomy Observatory. YYK is currently a Research Fellow of the Alexander von Humboldt Foundation. DCH was partially supported by an award from the Research Corporation. MK was supported in part through a stipend from the International Max Planck Research School for Radio Astronomy at the University of Bonn and, in part, by a NASA Postdoctoral Program Fellowship appointment at the Goddard Space Flight Center. The MOJAVE project is supported under National Science Foundation grant AST-0406923 and a grant from the Purdue Research Foundation. The work at the RATAN-600 radio telescope was supported by the Russian Ministry of Education and Science, the NASA JURRISS Program (project W-19611), and the Russian Foundation for Basic Research (grants 01-02-16812 and 05-02-17377). The University of Michigan Radio Astronomy Observatory is supported by the University of Michigan and the National Science Foundation (grant AST- 0607523).

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