Structure of the accretion flow in broad-line radio galaxies: The case of 3C 390.3

R. M. Sambruna, J. N. Reeves, V. Braito, K. T. Lewis, M. Eracleous, M. Gliozzi, F. Tavecchio, D. R. Ballantyne, P. M. Ogle, A. J. Barth, J. Tueller

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Abstract

We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C390.3 acquired in 2004 October and 2006 December, respectively. An archival Swift BAT spectrum from the 9 month survey is also analyzed, as well as an optical spectrum simultaneous to XMM-Newton. At soft X-rays, no absorption features are detected in the Reflection Grating Spectrometer spectrum of 3C390.3; a narrow emission line is found at 0.564keV, most likely originating in the narrow-line region. Both the EPIC and XIS data sets confirm the presence of an FeKα emission line at 6.4keV with equivalent width (EW) = 40eV. The FeKα line has a width FWHM ∼ 8800kms-1, consistent within a factor of 2with the width of the double-peaked Hα line, suggesting an origin from the broad-line region. The data show for the first time a weak, broad bump extending from 5 to 7keV. When fitted with a Gaussian, its centroid energy is 6.6keV in the source's rest frame with FWHM of 43,000km s-1 and EW of 50eV; its most likely interpretation is emission from He-like Fe(FeXXV), suggesting the presence of an ionized medium in the inner regions of 3C390.3. The broadband 0.5-100keV continuum is well described by a single power law with photon index Γ = 1.6 and cutoff energy 157keV, plus cold reflection with strength R = 0.5. In addition, ionized reflection is required to account for the 6.6keV bump in the broadband continuum, yielding an ionization parameter ξ ∼ 2700 erg cm s-1; the inner radius of the ionized reflector is constrained to be larger than 20rG , although this result depends on the assumed emissivity profile of the disk. If true, we argue that the lack of broad FeK emission from within 20rG indicates that the innermost regions of the disk in 3C390.3 are obscured and/or poorly illuminated. While the spectral energy distribution (SED) of 3C390.3 is generally dominated by accretion-related continuum, during accretion low states the jet can significantly contribute in the optical to X-ray bands via synchrotron self-Compton emission. The Compton component is expected to extend to and peak at GeV gamma rays where it will be detected with the Fermi Gamma-Ray Space Telescope during its first few years of operation.

Original languageEnglish (US)
Pages (from-to)1473-1487
Number of pages15
JournalAstrophysical Journal
Volume700
Issue number2
DOIs
StatePublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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