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Published November 20, 2011 | Published
Journal Article Open

γ-Ray and Parsec-scale Jet Properties of a Complete Sample of Blazars From the Mojave Program


We investigate the Fermi Large Area Telescope γ-ray and 15 GHz Very Long Baseline Array radio properties of a joint γ-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination –30° during this period, and thus probes the full range of γ-ray loudness (γ-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing γ-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the γ-ray emission in these BL Lac objects over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED-peak-γ-ray-loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQs) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lac objects have generally lower Doppler factors than the lower-synchrotron peaked BL Lac objects or FSRQs in our sample.

Additional Information

© 2011 The American Astronomical Society. Received 2011 July 22; accepted 2011 August 26; published 2011 November 2. We thank M. H. Cohen and D. C. Homan for helpful comments on the manuscript. C. S. Chang was a former member of the International Max Planck Research School for Astronomy and Astrophysics. C. S. Chang acknowledges support by the EU Framework 6 Marie Curie Early Stage Training programme under contract number MEST-CT-2005-19669 "Estrela." Y. Y. Kovalev was supported in part by the return fellowship of the Alexander von Humboldt Foundation and the Russian Foundation for Basic Research (RFBR) grants 08-02-00545 and 11-02-00368. E. Ros acknowledges partial support by the Spanish MICINN through grant AYA2009-13036-C02-02. Work at UMRAO was made possible by grants from the NSF and NASA and by support from the University of Michigan. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d' Études Spatiales in France. The MOJAVE project is supported under National Science Foundation grant AST-0807860 and NASA Fermi grant NNX08AV67G. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work made use of the Swinburne University of Technology software correlator (Deller et al. 2011), developed as part of the Australian Major National Research Facilities Programme and operated under licence. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The VLBA is a facility of the National Science Foundation operated by the National Radio Astronomy Observatory under cooperative agreement with Associated Universities, Inc. Facilities: VLBA, Fermi(LAT), UMRAO, OVRO:40m

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