The Discovery of an O VII Emission Line in the ASCA Spectrum of the Seyfert Galaxy NGC 3783
Abstract
We report the first observation of an O VII 0.57 keV emission line in a Seyfert 1 galaxy. NGC 3783 was observed by ASCA twice over a period of 4 days in 1993 December. The source exhibited a ~30% change in intensity between the two observations, with most of the variability taking place as a result of steepening of the continuum <~1 keV. Spectra from both observations show intense absorption features in the 0.5-1.5 keV band, which can be well fitted by an ionized absorber model of solar composition, column density of 10^22.2^ cm^-2^ and ionization parameter of ~7-8; the strongest absorption features being due to O VII and O VIII Two emission features are also seen in the spectra which we identify as O VII 0.57 keV (equivalent width ~36 eV) and O VIII 0.65 keV (equivalent width ~11 eV). We find these features are at the intensity predicted by the above ionized absorber model when the covering factor is close to unity. We also show that the 3-6 keV continuum of the source is well fitted by a {GAMMA} = 1.3-1.4 power-law continuum, a narrow neutral iron K-shell fluorescence line and a strong iron K-shell absorption edge, possibly corresponding to highly ionized iron. The intensity of neither of these K-shell features can be explained by the ionized absorber, and thus must be from a separate component.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 1995
- DOI:
- 10.1086/187717
- Bibcode:
- 1995ApJ...438L..67G
- Keywords:
-
- Galactic Nuclei;
- K Lines;
- Red Shift;
- Seyfert Galaxies;
- Spectrum Analysis;
- X Ray Astronomy;
- X Ray Sources;
- X Ray Spectra;
- Continuum Mechanics;
- Imaging Spectrometers;
- Mathematical Models;
- Power Series;
- Solid State Devices;
- Stellar Models;
- Astronomy;
- GALAXIES: ACTIVE;
- GALAXIES: NUCLEI;
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 3783;
- X-RAYS: GALAXIES