Volume 512, March-April 2010
|Number of page(s)||6|
|Published online||24 March 2010|
Relativistic beaming and gamma-ray brightness of blazars
Max-Planck-Institut für Radioastronomie, Auf dem
Hügel 69, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 Department of Physics and Astronomy, Denison University, Granville, OH 43023, USA
3 Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
4 Metsähovi Radio Observatory, Helsinki University of Technology TKK, Metsähovintie 114, 02540 Kylmälä, Finland
5 Dr. Karl Remeis-Observatory & ECAP, Friedrich-Alexander University Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany
6 CRESST/NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
7 Universities Space Research Association, 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA
8 Astro Space Center of Lebedev Physical Institute, Profsoyuznaya 84/32, 117997 Moscow, Russia
9 Departament d'Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, Valencia, Spain
Accepted: 12 January 2010
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 millimetre-wavelength flux density monitoring data from Metsähovi 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.
Key words: galaxies: active / galaxies: jets / quasars: general / BL Lacertae objects: general
© ESO, 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.