The intrinsic line width of the Fe K α line of AGN

X-ray fluorescent lines are unique features of the reflection spectrum of the cold torus when irradiated by the central AGN. Their intrinsic line widths can be used to probe the line-emitting region. The line widths of the Fe K alpha line measured from the first-order Chandra High Energy Grating (HEG) spectra are 3-5 times larger than those measured with the Si K alpha line for Circinus, Mrk 3, and NGC 1068. Because the observed Si K alpha and Fe K alpha lines are not necessarily coming from the same physical region, it is uncertain whether the line widths of the Fe K alpha line are overestimated or not. We measured the intrinsic line widths of the Fe K alpha line of several nearby bright AGN using the second- and third-order Chandra HEG spectra, whose spectral resolutions are better than the first-order data. We found the measured widths are all smaller than those from the first-order data. The results clearly show that the widths of the Fe K alpha line measured from the first-order HEG data are overestimated. It indicates that the Fe K alpha lines of the studied sources are originating from regions around the cold dusty torus.