NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-19 T14:21:44 PDT
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For refcode 1994A&A...283...51T:
Retrieve 41 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1994A&A...283...51T Brightness temperatures and viewing angles for extragalactic radio sources: a test of unification schemes for active galactic nuclei H. Terasranta and E. Valtaoja Metsahovi Radio Research Station, Helsinki University of Technology, SF- 02540 Kylmala, Finland Tuorla Observaton, University of Turku, SF-21500 Piikkio, Finland Received 2 February 1993/Accepted 20 June 1993 Abstract. We use 22 and 37 GHz continuum flux data from the Metsahovi monitoring program to derive variability timescales and associated brightness temperatures for a flux-limited sample of 41 quasars, BL lacs and radio galaxies. Even with H_0_ = 100 km/s/Mpc, about half of the sources have had at least one outburst exceeding the synchrotron limit T_b_ ~ 10^12^K, indicating the need for relativistic boosting. The T_b_- distributions for various classes of AGN are different, with highly polarized (blazar-type) quasars generally having the highest brightness temperatures, followed by low polarization (ordinary) quasars and finally radio galaxies. We argue that this results from different average viewing angles, in accordance with orientation-dependent unification schemes for active galactic nuclei. We have further calculated the viewing angle {theta} for the sources with measured apparent VLBI expansion speeds. We find that a radio galaxy appears as a quasar if the viewing angle is <~ 35^deg^ and as a highly polarized quasar (blazar) if {theta} <~18^deg. For this radio galaxy / QSO population the intrinsic Lorentz factor {GAMMA} ranges between 10 and 40. BL Lacs come from a different parent population with 4 <~ {GAMMA} <~ 12 and {theta} <~ 40^deg^. The small superluminal expansion speeds of BL Lacs are due to smaller Lorentz factors, not especially small viewing angles. Key words: galaxies: active- BL Lac objects: general -quasars: general - radio continuum: galaxies
Retrieve 41 NED objects in this reference.
Please click here for ADS abstract

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