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RESEARCH PRODUCT

Relativistic beaming and gamma-ray brightness of blazars

J. A. ZensusTuomas SavolainenDaniel C. HomanMatthias KadlerTalvikki HovattaMatthew L. ListerYuri Y. KovalevYuri Y. KovalevEduardo RosEduardo Ros

subject

BrightnessCosmology and Nongalactic Astrophysics (astro-ph.CO)Astrophysics::High Energy Astrophysical Phenomenajets [galaxies]FOS: Physical sciencesAstrophysicsAstrophysics::Cosmology and Extragalactic Astrophysics01 natural scienceslaw.inventionTelescopesymbols.namesakeRelativistic beaminglawquasars: general0103 physical sciencesBlazar010303 astronomy & astrophysicsUNESCO::ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia::GalaxiasHigh Energy Astrophysical Phenomena (astro-ph.HE)Physicsgeneral [quasars]general [BL Lacertae objects]010308 nuclear & particles physicsGamma rayAstronomy and Astrophysicsgalaxies: jetsViewing angle:ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia [UNESCO]:ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogonia::Galaxias [UNESCO]Lorentz factorSpace and Planetary Scienceactive [galaxies]BL Lacertae objectssymbolsUNESCO::ASTRONOMÍA Y ASTROFÍSICA::Cosmología y cosmogoniaAstrophysics - High Energy Astrophysical Phenomenagalaxies: active; ; ; BL Lacertae objects : generalFermi Gamma-ray Space TelescopeAstrophysics - Cosmology and Nongalactic Astrophysics

description

We investigate the dependence of gamma-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. By combining apparent jet speeds derived from high-resolution VLBA images from the MOJAVE program with millimetre-wavelength 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 gamma-rays by the Fermi Large Area Telescope (LAT) during its first three months of science operations and those which were not detected. 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 gamma-ray bright and weak sources. Most interestingly, gamma-ray bright blazars have a distribution of comoving frame viewing angles that is significantly narrower than that of gamma-ray weak blazars and centred roughly perpendicular to the jet axis. The lack of gamma-ray bright blazars at large comoving frame viewing angles can be explained by relativistic beaming of gamma-rays, while the apparent lack of gamma-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 gamma-ray emission.

yearjournalcountryeditionlanguage
2009-11-25
10.1051/0004-6361/200913740http://arxiv.org/abs/0911.4924