The Discovery of an O VII Emission Line in the ASCA Spectrum of the
Seyfert Galaxy NGC 3783
Authors:
George, I.M.,
Turner, T.J.,
Netzer, H.,
Journal: ApJL, 438, L67
Publication Date: 1995 Jan 10
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 a 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 fit by an ionized absorber model of
solar composition, column density of 10E22.2 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 in seen the spectra
which we identify as O OVII 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 souce 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.
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George, Turner, Netzer, 1995, ApJL, 438, L67
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