Relativistic beaming and gamma-ray brightness of blazars

By T. Savolainen, D. Homan, T. Hovatta, M. Kadler, Y. Kovalev, M. Lister, E. Ros, J. Zensus. 2009

196 citations recorded by the source corpus.

Aims. We investigate the dependence of γ-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. Methods. By combining apparent jet speeds derived from high-resolution VLBA images from the MOJAVE program with millimetrewavelength flux density monitoring data from Metsahovi Radio Observatory, we estimate the jet Doppler factors, Lorentz factors, and viewing angles for a sample of 62 blazars. We study the trends in these quantities between the sources which were detected in γ-rays by the Fermi Large Area Telescope (LAT) during its first three months of science operations and those which were not detected. Results. The LAT-detected blazars have on average higher Doppler factors than non-LAT-detected blazars, as has been implied indirectly in several earlier studies. We find statistically significant differences in the viewing angle distributions between γ-ray bright and weak sources. Most interestingly, γ-ray bright blazars have a distribution of comoving frame viewing angles that is significantly narrower than that of γ-ray weak blazars and centred roughly perpendicular to the jet axis. The lack of γ-ray bright blazars at large comoving frame viewing angles can be explained by relativistic beaming of γ-rays, while the apparent lack of γ-ray bright blazars at small comoving frame viewing angles, if confirmed with larger samples, may suggest an intrinsic anisotropy or Lorentz factor dependence of the γ-ray emission.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/e074d935f9902f84d788301f051dbea1dbc6802c

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Citations in the corpus

Reconnection-driven plasmoids in blazars: fast flares on a slow envelope (2012, background): “This is much larger than the Lorentz factorΓ j ∼ 10 − 20 typically inferred for blazar jets from superluminal motions (see, e.g., Savolainen et al. 2010).”
THE LUMINOSITY FUNCTION OF FERMI-DETECTED FLAT-SPECTRUM RADIO QUASARS (2011, methodology): “Monitoring observations with the Very Long Baseline Array (VLBA) established that LAT-detected blazars have, on average, signiﬁcantly faster apparent jet speeds than non-LAT detected blazars (Lister et al. 2009a; Savolainen et al. 2010).”
MOJAVE: Monitoring of Jets in Active galactic nuclei with VLBA Experiments (2012, background): “◦4 (Savolainen et al. 2010), respectively, and in turn to overestimated magnetic field strengths.”
THE COSMIC EVOLUTION OF FERMI BL LACERTAE OBJECTS (2013, result): “Moreover, in agreement with the observation of BL Lacs in radio (e.g. Lähteenmäki & Valtaoja 2003; Lister et al. 2009; Savolainen et al. 2010), we set γa = 2 which is lower than the minimum value used (and found) for FSRQs (see e.g. Ajello et al. 2012).”
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).”
Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program (2017, result): “…motion in their jets is somehow hidden from us, given the results of several studies finding that γ-ray sources have higher Doppler factors on average than the general population of AGN (e.g., Jorstad et al. 2001a; Lähteenmäki & Valtaoja 2003; Savolainen et al. 2010; Lister et al. 2016).”
Non-thermal particle acceleration in collisionless relativistic electron-proton reconnection (2016, background): “…to a frequency of the observed synchrotron peak ∼ 1015BGΓj Hz, where BG is the co-moving magnetic field in the emitting region, measured in Gauss, and Γj is the Doppler boost due to the bulk Lorentz factor of the jet, which typically lies in the range Γj ∼ 10−40 (Savolainen et al. 2010).”