FeK line profile in low-redshift quasars: Average shape and Eddington ratio dependence

We analyze X-ray spectra of 43 Palomar-Green quasars observed with XMM-Newton in order to investigate their mean Fe K line profile and its dependence on physical properties. The continuum spectra of 39 objects are well reproduced by a model consisting of a power law and a blackbody modified by Galactic absorption. The spectra of the remaining four objects require an additional power-law component absorbed with a column density of similar to 10(23) cm(-2). A feature resembling an emission line at 6.4 keV, identified with an Fe K line, is detected in 33 objects. Approximately half of the sample show an absorption feature around 0.65-0.95 keV, which is due to absorption lines and edges of O VII and O VIII. We fit the entire sample simultaneously to derive average Fe line parameters by assuming a common Fe line shape. The Fe line is relatively narrow ( sigma = 0.36 keV), with a center energy of 6.48 keV and a mean equivalent width ( EW) of 248 eV. By combining black hole masses estimated from the virial method and bolometric luminosities derived from full spectral energy distributions, we examine the dependence of the Fe K line profile on the Eddington ratio. As the Eddington ratio increases, the line becomes systematically stronger ( EW = 130-280 eV) and broader ( sigma = 0.1-0.7 keV), and peaks at higher energies ( 6.4-6.8 keV). This result suggests that the accretion rate onto the black hole directly influences the geometrical structure and ionization state of the accretion disk.