ASCA OBSERVATIONS OF SEYFERT-1 GALAXIES .2. RELATIVISTIC IRON K-ALPHAEMISSION

We present evidence for widespread relativistic effects in the central regions of active galactic nuclei. In a sample of 18 Seyfert 1 galaxi es observed by ASCA, 14 show an iron Ka line that is resolved, with me an width sigma(K alpha) = 0.43 +/- 0.12 keV for a Gaussian profile (fu ll, width at half-maximum, FWHM similar to 50,000 km s(-1)). However, many of the line profiles are asymmetric. A strong red wing is indicat ive of gravitational redshifts close to a central black hole, and accr etion disk models provide an excellent description of the data. The pe ak energy of the line is 6.4 keV, which indicates that it arises by fl uorescence in near-neutral material. Our Ms imply a low inclination fo r the disk in these Seyfert 1 galaxies, with a mean of 30 degrees, con sistent with orientation-dependent unification schemes. Differences in the line profiles from source to source imply slight variations in ge ometry, which cannot be accounted for solely by inclination. In most c ases, 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 littl e effect on our conclusions regarding the disk line. Our data are fit equally well with rotating (Kerr) and nonrotating (Schwarzschild) blac k hole models. We find a mean spectral index in the 3-10 keV range of [Gamma(3-10)] = 1.91 +/- 0.07 after accounting for the effects of refl ection. Such observations probe the innermost regions of active galact ic nuclei and arguably provide the best evidence yet obtained for the existence of supermassive black holes in the centers of active galaxie s.