Discovery of narrow x-ray absorption lines from NGC 3783 with the chandra high energy transmission grating spectrometer

Shai Kaspi, W. N. Brandt, Hagai Netzer, Rita Sambruna, George Chartas, Gordon P. Garmire, John A. Nousek

Research output: Contribution to journalArticlepeer-review


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 kilometers per second 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 s21 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.

Original languageEnglish
Pages (from-to)L17-L20
JournalAstrophysical Journal Letters
Issue number1
StatePublished - 20 May 2000


  • Galaxies: Active
  • Galaxies: Individual (NGC 3783)
  • Galaxies: Seyfert
  • Galaxies: nuclei
  • Techniques: Spectroscopic
  • X-rays: Galaxies


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