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

Abstract

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.

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

“…Variability arguments (Jorstad et al 2005;Hovatta et al 2009) and kinematical analyses (Cohen et al 2015) yield a remarkably consistent value of 7.2 d = , from which we estimate a lower limit of the intrinsic brightness temperature in the core component of our RadioAstron observations of T b,int > 2.9 10 12 K. >´K, derived for the core component of the source structure described in Table 2 =´K is calculated from the data on the same baselines.…”

“…In this model, the intrinsic brightness temperatures cannot exceed 10 11 -10 12 K (Kellermann & Pauliny-Toth 1969;Readhead 1994). Typical Doppler boosting is expected to be able to raise this temperature by a factor of ∼10 (see also Hovatta et al 2009;Lister et al 2013). For direct interferometric measurements, increasing the interferometer baseline length is the only way to measure higher brightness temperatures (see, e.g., Kovalev et al 2005), and hence, to place stringent observational constraints on the physics of the most energetic relativistic outflows.…”

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

“…However, compact blazars such as those in our sample, often exhibiting brightness temperatures exceeding the 5 × 10 10 K equipartition limit (Readhead 1994;, are known from VLBI observations to have Doppler boosting factors ranging from δ ∼ 5 to 30 (e.g., Hovatta et al 2009), with median values of δ ∼15 and 6 for FSRQs and BL Lac objects respectively. These sources are thus capable of exhibiting significant structural variations on timescales of a few months.…”

The extension of variability properties in gamma-ray bursts to blazars

“…where a typical uncertainty of 0.4 dex and 0.2 dex is assigned for MTS of blazars (e.g., Vovk & Neronov 2013) and GRBs (e.g., Golkhou et al 2015), respectively, and a 50% or 30% error is introduced for Γ for GRBs (e.g., Lü et al 2012;Sonbas et al 2014) and blazars (e.g., Hovatta et al 2009), respectively. It is found that the global slope for blazars/GRBs is roughly consistent with that found in 21 GRBs only within uncertainties.…”