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

Abstract

We extend the study of the core of the Fe K$\\alpha$ emission line at \\sim 6.4\nkeV in Seyfert galaxies reported in Yaqoob &amp; Padmanabhan (2004) using a larger\nsample observed by the Chandra High Energy Grating (HEG). Whilst heavily\nobscured active galactic nuclei (AGNs) are excluded from the sample, these data\noffer some of the highest precision measurements of the peak energy of the Fe\nK$\\alpha$ line, and the highest spectral resolution measurements of the width\nof the core of the line in unobscured and moderately obscured ($N_{H}&lt;10^{23} \\\n\\rm cm^{-2}$) Seyfert galaxies to date. The Fe K$\\alpha$ line is detected in 33\nsources, and its centroid energy is constrained in 32 sources. In 27 sources\nthe statistical quality of the data is good enough to yield measurements of the\nFWHM. We find that the distribution in the line centroid energy is strongly\npeaked around the value for neutral Fe, with over 80% of the observations\ngiving values in the range 6.38--6.43 keV. Including statistical errors, 30 out\nof 32 sources ($\\sim 94%$) have a line centroid energy in the range 6.35--6.47\nkeV. The mean equivalent width, amongst the observations in which a non-zero\nlower limit could be measured, was $53 \\pm 3eV. The mean FWHM from the\nsubsample of 27 sources was $2060 \\pm 230 \\ \\rm km \\ s^{-1}$. The mean EW and\nFWHM are somewhat higher when multiple observations for a given source are\naveraged. From a comparison with the H$\\beta$ optical emission-line widths (or,\nfor one source, Br$\\alpha$), we find that there is no universal location of the\nFe K$\\alpha$ line-emitting region relative to the optical BLR. We confirm the\npresence of the X-ray Baldwin effect, an anti-correlation between the Fe\nK$\\alpha$ line EW and X-ray continuum luminosity. The HEG data have enabled\nisolation of this effect to the narrow core of the Fe K$\\alpha$ line.\n