Detection of Asymmetry in the Narrow Fe K$α$ Emission Line in MCG-5-23-16 with Chandra

Abstract: Iron K$\alpha$ (Fe K$\alpha$) emission is observed ubiquitously in AGN, and it is a powerful probe of their circumnuclear environment. Examinations of the emission line play a pivotal role in understanding the disk geometry surrounding the black hole. It has been suggested that the torus and the broad line region (BLR) are the origins of emission. However, there is no universal location for the emitting region relative to the BLR. Here, we present an analysis of the narrow component of the Fe K$\alpha$ line in the Seyfert AGN MCG-5-23-16, one of the brightest AGN in X-rays and in Fe K$\alpha$ emission, to localize the emitting region. Spectra derived from Chandra/HETGS observations show asymmetry in the narrow Fe K$\alpha$ line, which has only been confirmed before in the AGN NGC 4151. Models including relativistic Doppler broadening and gravitational redshifts are preferred over simple Gaussians and measure radii consistent with $R \simeq$ 200-650 r$_g$. These results are consistent with those of NGC 4151 and indicate that the narrow Fe K$\alpha$ line in MCG-5-23-16 is primarily excited in the innermost part of the optical broad line region (BLR), or X-ray BLR. Characterizing the properties of the narrow Fe K$\alpha$ line is essential for studying the disk geometries of the AGN population and mapping their innermost regions.