Discovery of Narrow X-ray Absorption Lines from Ngc 3783 with the Chandra Hetgs

We present the first grating-resolution X-ray spectra of the Seyfert 1 galaxy NGC 3783, obtained with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory. These spectra reveal many narrow absorption lines from the H-like and He-like ions of O, Ne, Mg, Si, S and Ar, as well as Fe XVII–Fe XXI L-shell lines. We have also identified several weak emission lines, mainly from O and Ne. The absorption lines are blueshifted by a mean velocity of ≈ 440± 200 km s−1 and are not resolved, indicating a velocity dispersion within the absorbing gas of a few hundred km s−1 or less. We measure the lines’ equivalent widths and compare them with the predictions of photoionization models. The best-fitting model has a microturbulence velocity of 150 km s−1 and a hydrogen column density of 1.3× 1022 cm−2. The measured blueshifts and inferred velocity dispersions of the X-ray absorption lines are consistent with those of the strongest UV absorption lines observed in this object. However, simple models that propose to strictly unify the X-ray and UV absorbers have difficulty explaining simultaneously the X-ray and UV absorption line strengths. Subject headings: galaxies: active — galaxies: nuclei — galaxies: Seyfert — galaxies: individual (NGC 3783) — X-rays: galaxies — techniques: spectroscopic