High-resolution X-ray spectroscopy of the Seyfert 2 galaxy Circinus with Chandra

Results from a 60 ks Chandra High-Energy Transmission Grating Spectrometer observation of the nearby Seyfert 2 galaxy Circinus are presented. The spectrum shows a wealth of emission lines at both soft and hard X-rays, including lines of Ne, Mg, Si, S, Ar, Ca, and Fe, and a prominent Fe K alpha line at 6.4 keV. We identify several of the He-like components and measure several of the Lyman lines of the H-like ions. The lines' profiles are unresolved at the limited signal-to-noise ratio of the data. Our analysis of the zero-order image in a companion Letter constrains the size of the emission region to be 20-60 pc, suggesting that emission within this volume is almost entirely due to the reprocessing of the obscured central source. Here we show that a model containing two distinct components can reproduce almost all the observed properties of this gas. The ionized component can explain the observed intensities of the ionized species, assuming twice-solar composition and an N proportional to r(-1.5) density distribution. The neutral component is highly concentrated, well within the 0.8 " point source, and is responsible for almost all of the observed K alpha (6.4 keV) emission. Circinus seems to be different than Mrk 3 in terms of its gas distribution.