4.7 Article

THE SPECTRAL ENERGY DISTRIBUTION OF FERMI BRIGHT BLAZARS

期刊

ASTROPHYSICAL JOURNAL
卷 716, 期 1, 页码 30-70

出版社

IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/716/1/30

关键词

BL Lacertae objects: general; galaxies: active; gamma rays: galaxies; quasars: general; radiation mechanisms: non-thermal

资金

  1. Fermi-LAT Collaboration
  2. National Aeronautics and Space Administration
  3. Department of Energy in the United States
  4. Commissariat a l'Energie Atomique
  5. Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France
  6. Agenzia Spaziale Italiana
  7. Istituto Nazionale di Fisica Nucleare in Italy
  8. Ministry of Education, Culture, Sports, Science and Technology (MEXT)
  9. High Energy Accelerator Research Organization (KEK)
  10. Japan Aerospace Exploration Agency (JAXA) in Japan
  11. K. A. Wallenberg Foundation
  12. Swedish Research Council
  13. Swedish National Space Board in Sweden
  14. Istituto Nazionale di Astrofisica in Italy
  15. K. A. Wallenberg Foundation in Sweden
  16. Russian Foundation for Basic Research [01-02-6812, 08-02-00545]
  17. Georgian National Science Foundation [GNSF/ST-08/4-404]
  18. Smithsonian Institution
  19. Academia Sinica. St. Petersburg University
  20. Russian RFBR foundation [09-02-00092]
  21. ICREA Funding Source: Custom
  22. UK Space Agency [ST/G008655/1] Funding Source: researchfish
  23. Division Of Astronomical Sciences
  24. Direct For Mathematical & Physical Scien [808050] Funding Source: National Science Foundation

向作者/读者索取更多资源

We have conducted a detailed investigation of the broadband spectral properties of the gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/gamma-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 gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log nu-log nu F-nu 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, alpha(ro), and optical to X-ray, alpha(ox), spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency (nu(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 gamma-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 gamma-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 gamma-ray sources, the correlation between nu(S)(peak) and gamma-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.

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