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We present an analysis of the X-ray spectra of a sample of 37 observations of 26 Seyfert galaxies observed by XMM-Newton in order to characterize their iron K emission. All objects show evidence for iron line emission in the 6-7 keV band. A narrow core at 6.4 keV is seen almost universally in the spectra, and we model this using a neutral Compton reflection component, assumed to be associated with distant, optically thick material such as the molecular torus. Once this, and absorption by a zone of ionized gas in the line-of-sight is accounted for, less than half of the sample observations show an acceptable fit. Approximately 2/3 of the sample shows evidence for further, broadened emission in the iron K-band. When modeled with a Gaussian, the inferred energy is close to that expected for neutral iron, with a slight redshift, with an average velocity width of ~0.1c. The mean parameters are consistent with previous ASCA results and support the idea that the broad components can be associated with the accretion disk. Before proceeding to that conclusion, we test an alternative model comprising a blend of 3-4 narrow, unshifted emission lines (including the 6.4 keV core), together with 1-2 zones of highly ionized gas in the line-of-sight. Around 1/3 of the objects are not adequately fit by this model, and in general better fits are obtained with a relativistic disk line model, which has fewer free parameters. Nonetheless we find that absorption by ionized gas affects the spectrum above 2.5 keV in approximately half the sample. There is evidence for multiple ionized zones in at least 3 objects, but in all those cases a blurred reflector is required in addition to the complex absorption. (truncated)Comment: 36 pages, 13 figures, accepted for publication in MNRA

We present evidence for widespread relativistic effects in the central regions of active galactic nuclei. In a sample of 18 Seyfert 1 galaxies observed by ASCA, 14 show an iron Kα line which is is resolved, with mean width σ Kα = 0.43 ± 0.12 keV for a gaussian profile (Full Width at Half Maximum, FWHM∼ 50, 000 km s −1 ). However, many of the line profiles are asymmetric. A strong red wing is indicative of gravitational redshifts close to a central black hole and accretion disk models provide an excellent description of the data.The peak energy of the line is 6.4 keV, indicating that it arises by fluorescence in near-neutral material. Our fits imply a low inclination for the disk in these Seyfert 1 galaxies, with a mean of 30 • , consistent with orientation-dependent unification schemes. Differences in the line profiles from source-to-source imply slight variations in geometry, which cannot be accounted for solely by inclination. In most cases, we require that the line emission arises from a range of radii. Although a small contribution to the emission from a region other than the disk is not ruled out, it is not generally required and has little effect on our conclusions regarding the disk line. Our data are fit equally well with rotating (Kerr) and non-rotating (Schwarzschild) black hole models. We find a mean spectral index in the 3-10 keV range of < Γ 3−10 >= 1.91 ± 0.07 after accounting for the effects of reflection.Such observations probe the innermost regions of AGN, and arguably provide the best evidence yet obtained for the existence of super-massive black holes in the centers of active galaxies.