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The discovery of an O VII emission line in the ASCA spectrum of the Seyfert galaxy NGC 3783We 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 approximately 30% change in intensity between the two observations, with most of the variability taking place as a result of steepening of the continuum less than or approximately equal to 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(exp 22.2)/sq cm and ionization parameter of approximately 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 approximately equals 36 eV) and O VIII 0.65 keV (equivalent width approximately equals 11 eV). 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.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
George, I. M. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Turner, T. J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Netzer, H. (Tel Aviv Univ. Tel Aviv, Israel)
Date Acquired
August 16, 2013
Publication Date
January 10, 1995
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 438
Issue: 2
ISSN: 0004-637X
Subject Category
Funding Number(s)
Distribution Limits