The Correlation between X-ray spectral slope and FeKalpha line energy in radio-quiet active galactic nuclei

Abstract

A significant correlation between FeKalpha line energy and X-ray spectral slope has been discovered among radio-quiet active galactic nuclei. The ionization stage of the bulk of the FeKalpha emitting material is not the same in all active galactic nuclei and is related to the shape of the X-ray continua. Active galactic nuclei with a steep X-ray spectrum tend to have a fluorescence FeKalpha line from highly ionized material. In the narrow-line Seyfert 1 galaxies with steeper X-ray spectrum (Gamma_X > 2.1), the FeKalpha line originates from highly ionized material. In the Seyfert 1 galaxies and quasars with flatter X-ray spectrum (Gamma_X < 2.1), bulk of the FeKalpha emission arises from near neutral or weakly ionized material. The correlation is an important observational characteristic related to the accretion process in radio quiet active galactic nuclei and is driven by a fundamental physical parameter which is likely to be the accretion rate relative to the Eddington rate.Comment: 4 pages, To apear in ApJ Letter