2005ApJ...627..156Y

We report on the results of detailed X-ray spectroscopy of the Fe K region in the Seyfert 1 galaxy NGC 3783 using the Chandra High Energy Grating Transmission Spectrometer (HETGS). There were five observations over an interval of ∼125 days in 2001, each with an exposure time of ∼170 ks. The combined data constitute the highest signal-to-noise Fe K spectrum having the best velocity resolution in the Fe K band to date (FWHM∼1860 km/s). The combined data show a resolved Fe Kα line core (FWHM=1700⁺⁴¹⁰_–390 km/s) with a center energy of 6.397±0.003 keV, consistent with an origin in neutral or lowly ionized Fe, located between the BLR and NLR, as found by Kaspi et al. in 2002. We also find that excess flux around the base of the Fe Kα line core can be modeled with either a Compton-scattering ``shoulder'' or an emission line (with about the same flux as the line core) from a relativistic accretion disk, having an inclination angle of 11° or less. This disk-line model is as good as a Compton-shoulder model for the base of the Fe Kα line core. In the latter model, we measured the column density to be 7.5^+2.7_–0.6x10²³/cm2, which corresponds to a Thomson optical depth of ∼0.60, so the line-emitting matter is not quite Compton-thick. An intrinsic width of 1500⁺⁴⁶⁰_–340km/s FWHM is still required in this model. Moreover, more complicated scenarios involving both a Compton shoulder and a disk line cannot be ruled out. We confirm an absorption feature due to He-like Fe (FWHM=6405⁺⁵⁰²⁰_–2670km/s) found in previous studies.