Abdo, A. A. and Max-Moerbeck, W. and Pavlidou, V. and Richards, J. L. and Stevenson, M. (2010) The Spectral Energy Distribution of Fermi Bright Blazars. Astrophysical Journal, 716 (1). pp. 30-70. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20100618-070754680
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We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν F _ν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, α_(ro), and optical to X-ray, α_(ox), spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (ν^S _(peak)) is positioned between 10^(12.5) and 10^(14.5) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10^(13) and 10^(17) Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between ν ^S _(peak) and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars.
|Additional Information:||© 2010 The American Astronomical Society. Received 2009 December 4; accepted 2010 March 27; published 2010 May 13. The Fermi-LAT Collaboration acknowledges the generous support of a number of agencies and institutes that have supported the Fermi-LAT Collaboration. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat `a l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucl´eaire 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 from the following agencies is also gratefully acknowledged: the Istituto Nazionale di Astrofisica in Italy and the K. A. Wallenberg Foundation in Sweden. This research is based also on observations with the 100 m telescope of the MPIfR (Max-Planck-Institut f¨ur Radioastronomie) at Effelsberg. RATAN-600 observations are supported in part by the Russian Foundation for Basic Research (projects 01-02- 16812 and 08-02-00545). Part of this work was supported by Georgian National Science Foundation grant GNSF/ST-08/4- 404 The mid-infrared VISIR results are based on observations carried out at the European Southern Observatory under programmes ID 078.B-0366, 079.B-0448, and 081.B-0404. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. St. Petersburg University team acknowledges support from Russian RFBR foundation via grant 09-02-00092. AZT-24 observations are made within an agreement between Pulkovo, Rome, and Teramo observatories. We acknowledge the use of data and software facilities from the ASDC, managed by the Italian Space Agency (ASI). Part of this work is based on archival data and on bibliographic information obtained from the NASA/IPAC Extragalactic Database (NED) and from the Astrophysics Data System (ADS). Facilities: Effelsberg, Fermi, OVRO:40m, Swift, WEBT|
|Subject Keywords:||BL Lacertae objects: general; galaxies: active; gamma rays: galaxies; quasars: general; radiation mechanisms: non-thermal|
|Classification Code:||PACS: 98.54.Cm; 98.62.Qz; 95.30.Gv; 95.30.Ky|
|Official Citation:||A. A. Abdo et al 2010 ApJ 716 30 doi: 10.1088/0004-637X/716/1/30|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||18 Jun 2010 22:44|
|Last Modified:||26 Dec 2012 12:09|
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