Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
By T. Hovatta, E. Valtaoja, M. Tornikoski, A. Lähteenmäki. 2008
357 citations recorded by the source corpus.
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.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/82f09534d01d8bbfc43d98a88db800903fcbb163
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Citations in the corpus
- Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets (2009, methodology): “References: ∗Gabuzda et al. (1994); ∗∗Pushkarev & Gabuzda (1999); †Hovatta et al. (2009); ‡Jorstad et al. (2005).”
- Jet opening angles and gamma-ray brightness of AGN (2009, positive): “During the first three months of science operations, the LAT has made 205 high-confidence (> 10σ) detections of bright γ-ray sources, 116 of which were associated with high galactic latitude (|b| > 10◦) AGN (the LAT Bright AGN Sample together with 10 lower-confidence associations: LBAS-ext), as disc”
- A simplified view of blazars: clearing the fog around long‐standing selection effects (2011, methodology): “…factor, we assumed a mean value of 15, which was chosen to be consistent with the mean superluminal speed βapp ∼ 12 obtained by Lister et al. (2009), and with the typical Lorentz factor Γ ∼ 15 derived by Hovatta et al. (2009) (since for the angle that maximizes the apparent velocity δ ∼ βapp ∼ Γ).”
- Relativistic beaming and gamma-ray brightness of blazars (2009, methodology): “By combining equations 2 and 3 in Hovatta et al. (2009) one gets δvar = ( 1.47× 1013 ∆S maxd2L ν2∆t2(1+ z)Tb,int )1/3 , (1) where∆S max is the flare amplitude in Janskys,ν is the observing frequency in GHz,∆t is the timescale of the fastest flare in the source in days,dL is the luminosity distance…”
- Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program (2017, background): “Values of Tb,obs ∼ 5×1011-5×1012 K in the FSRQs and BLLacs can be explained as equipartition brightness temperatures amplified by relativistic boosting with Doppler factor δ, Tb,obs ∝ δTb,int, since δ can be as high as ∼50 in blazars (e.g., Hovatta et al. 2009).”
- GAMMA-RAY LIGHT CURVES AND VARIABILITY OF BRIGHT FERMI-DETECTED BLAZARS (2010, background): “Doppler factors D are taken from Hovatta et al. (2009) and Savolainen et al. (2010).”