EDP Sciences
Free access

This article has an erratum: [erratum]

Volume 494, Number 2, February I 2009
Page(s) 527 - 537
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:200811150
Published online 27 November 2008
A&A 494, 527-537 (2009)
DOI: 10.1051/0004-6361:200811150

Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies

T. Hovatta1, E. Valtaoja2, 3, M. Tornikoski1, and A. Lähteenmäki1

1  Metsähovi Radio Observatory, TKK, Helsinki University of Technology, Metsähovintie 114, 02540 Kylmälä, Finland
    e-mail: tho@kurp.hut.fi
2  Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
3  Department of Physics and Astronomy, University of Turku, Vesilinnantie 5, 20100 Turku, Finland

Received 14 October 2008 / Accepted 18 November 2008

Aims. We have calculated variability Doppler boosting factors, Lorentz factors, and viewing angles for a large sample of sources by using total flux density observations at 22 and 37 GHz and VLBI data.
Methods. We decomposed the flux curves into exponential flares and determined the variability brightness temperatures of the fastest flares. By assuming the same intrinsic brightness temperature for each source, we calculated the Doppler boosting factors for 87 sources. In addition we used new apparent jet speed data to calculate the Lorentz factors and viewing angles for 67 sources.
Results. We find that all quasars in our sample are Doppler-boosted and that the Doppler boosting factors of BL Lacertae objects are lower than of quasars. The new Lorentz factors are about twice as high as in earlier studies, which is mainly due to higher apparent speeds in our analyses. The jets of BL Lacertae objects are slower than of quasars. There are some extreme sources with very high derived Lorentz factors of the order of a hundred. These high Lorentz factors could be real. It is also possible that the sources exhibit such rapid flares that the fast variations have remained undetected in monitoring programmes, or else the sources have a complicated jet structure that is not amenable to our simple analysis. Almost all the sources are seen in a small viewing angle of less than 20 degrees. Our results follow the predictions of basic unification schemes for AGN.

Key words: galaxies: active -- galaxies: jets -- radio continuum: galaxies -- radiation mechanisms: non-thermal -- galaxies: quasars: general

© ESO 2009

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.