The intrinsic line width of the Fe Ka line of AGN

Abstract

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 \Ka line measured from the first order Chandra High Energy Grating (HEG) spectra are $3-5$ times larger than those measured with the Si \Ka line for Circinus, Mrk 3, and NGC 1068. Because the observed Si \Ka and Fe \Ka lines are not necessarily coming from the same physical region, it is uncertain whether the line widths of the Fe \Ka line are over-estimated or not. We measured the intrinsic line widths of the Fe \Ka 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 \Ka line measured from the first order HEG data are over-estimated. It indicates that the Fe \Ka lines of the studied sources are originating from regions around the cold dusty torus.