THE CORES OF THE Fe Kα LINES IN ACTIVE GALACTIC NUCLEI: AN EXTENDED CHANDRA HIGH ENERGY GRATING SAMPLE

We extend the study of the core of the Fe K alpha emission line at similar to 6.4 keV in Seyfert galaxies reported by Yaqoob & Padmanabhan using a larger sample observed by the Chandra high-energy grating (HEG). The sample consists of 82 observations of 36 unique sources with z < 0.3. Whilst heavily obscured active galactic nuclei are excluded from the sample, these data offer some of the highest precision measurements of the peak energy of the Fe K alpha line, and the highest spectral resolution measurements of the width of the core of the line in unobscured and moderately obscured (N-H < 10(23) cm(-2)) Seyfert galaxies to date. From an empirical and uniform analysis, we present measurements of the Fe K alpha line centroid energy, flux, equivalent width (EW), and intrinsic width (FWHM). The Fe K alpha line is detected in 33 sources, and its centroid energy is constrained in 32 sources. In 27 sources, the statistical quality of the data is good enough to yield measurements of the FWHM. We find that the distribution in the line centroid energy is strongly peaked around the value for neutral Fe, with over 80% of the observations giving values in the range 6.38-6.43 keV. Including statistical errors, 30 out of 32 sources (similar to 94%) have a line centroid energy in the range 6.35-6.47 keV. The mean EW, among the observations in which a non-zero lower limit could be measured, was 53 +/- 3 eV. The mean FWHM from the subsample of 27 sources was 2060 +/- 230 km s(-1). The mean EW and FWHM are somewhat higher when multiple observations for a given source are averaged. From a comparison with the H beta optical emission-line widths (or, for one source, Br alpha), we find that there is no universal location of the Fe K alpha line-emitting region relative to the optical broad-line region (BLR). In general, a given source may have contributions to the Fe K alpha line flux from parsec-scale distances from the putative black hole, down to matter a factor similar to 2 closer to the black hole than the BLR. We confirm the presence of the X-ray Baldwin effect, an anti-correlation between the Fe K alpha line EW and X-ray continuum luminosity. The HEG data have enabled isolation of this effect to the narrow core of the Fe K alpha line.