ASCAObservations of Seyfert 1 Galaxies. II. Relativistic Iron Kα Emission

Abstract

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.

Astrophysics in 1997

“…Several papers estimated or limited central black hole masses using indirect methods, including the shape of the big blue bump in the continuous spectrum (Wang & Zhou 1996), timescale of variability (Pesce et al 1997 and two following papers), rising central rotation curves (Keneko et al 1997), total luminosities (Di Matteo & Fabian 1997), velocity profiles (van den Bosch & de Zeeuw 1996), line asymmetries (Nandra et al 1997), and polarization (Lee & Blandford 1997). Possibly these tell us more about the opinion of the authors than about the galactic centers in question, but also that said opinion is overwhelmingly pro-black hole.…”

Observations of Seyfert Galaxies by OSSE and Parameters of Their X‐Ray/Gamma‐Ray Sources

“…The X-ray spectra of Seyfert gal-Z100 axies are known relatively well and consist (at keV) of Z2 power-law, Compton-reÑection, and Fe Ka components (e.g., Nandra & Pounds 1994 ;Nandra et al 1997 ;Zdziarski, & Smith 1999). However, the form of a Lubinski, high-energy cuto † of the power law remains poorly constrained.…”

Searching for Black Holes in Space

“…The following Japanese satellite, ASCA, obtained higher resolution spectra which showed the accompanying fluorescent Fe K line to have a broad red wing (Tanaka et al 1995, Nandra et al 1997, interpreted as a gravitational red shift and inspiring a major and continuing research effort to explore the effects of strong gravity in the inner parts of the accretion disc (Fabian et al 2000).…”