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

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 20r_G , 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 20r_G 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.