Fe K Line Profile in Low‐Redshift Quasars: Average Shape and Eddington Ratio Dependence

We analyze X-ray spectra of 43 Palomar-Green quasars observed with {\itXMM-Newton} in order to investigate their mean Fe K line profile and itsdependence on physical properties. The continuum spectra of 39 objects are wellreproduced by a model consisting of a power law and a blackbody modified byGalactic absorption. The spectra of the remaining four objects require anadditional power-law component absorbed with a column density of $\sim 10^{23}{\rm cm}^{-2}$. We fit the entire sample simultaneously to derive average Feline parameters by assuming a common Fe line shape. The Fe line is relativelynarrow ($\sigma=0.36$ keV), with a center energy of 6.48 keV and a meanequivalent width (EW) of 248 eV. By combining black hole masses estimated fromthe virial method and bolometric luminosities derived from full spectral energydistributions, we examine the dependence of the Fe K line profile on Eddingtonratio. As the Eddington ratio increases, the line becomes systematicallystronger (EW = 130 to 280 eV), broader ($\sigma=0.1$ to 0.7 keV), and peaks athigher energies (6.4 to 6.8 keV). This result suggests that the accretion rateonto the black hole directly influences the geometrical structure andionization state of the accretion disk.Comment: 12 pages, 9 figures, accepted for publication in the Astrophysical Journa