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

TL;DR

This study estimates Doppler boosting factors, Lorentz factors, and viewing angles for quasars, BL Lac objects, and radio galaxies using flux density and VLBI data, revealing relativistic jets aligned close to our line of sight.

Contribution

It provides new calculations of Lorentz factors and viewing angles, showing higher Lorentz factors than previous studies and confirming unification models for AGN.

Findings

Quasars are Doppler-boosted with small viewing angles.

BL Lac objects have lower Doppler factors and slower jets than quasars.

Some sources exhibit extremely high Lorentz factors, possibly due to rapid flares or complex jet structures.

Abstract

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. 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. 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.