NASA/IPAC EXTRAGALACTIC DATABASE
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For refcode 1999ApJ...521..493L:
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1999ApJ...521..493L Total Flux Density Variations in Extragalactic Radio Sources. III. Doppler Boosting Factors, Lorentz Factors, and Viewing Angles for Active Galactic Nuclei A. LAHTEENMAKI Metsahovi Radio Observatory, Helsinki University of Technology, FIN-02540 Kylmala, Finland; alien@kurp.hut.fi AND E. VALTAOJA Tuorla Observatory, University of Turku, FIN-21500 Piikkio, Finland Received 1998 December 23; accepted 1999 April 1 ABSTRACT We have calculated Doppler boosting factors, D_var_, for a sample of active galactic nuclei (AGNs) using total flux density variation monitoring data at 22 and 37 GHz. We argue that this method is more accurate than the other commonly used methods based on the synchrotron self-Compton X-ray flux or equipartition of energy. We compare our Doppler factors with other results and conclude that even if the average D_var_ for a class of sources is very similar to all others, the variability Doppler factors for individual objects are more accurate and reliable. An important application of precise Doppler factors is presented, namely, calculating the Lorentz factors, {GAMMA}, and the viewing angles, {theta}, of relativistic outflows in AGNs. We find that high-polarization quasars have the greatest Doppler boosting, while low-polarization quasars and BL Lac objects are less boosted. The two groups of quasars show different characteristics because of different combinations of the Lorentz factor and viewing angle, rather than either a different {GAMMA} or {theta} alone. Subject headings: galaxies: active-quasars: general-radiation mechanisms: nonthermal
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