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publication

An IRAS-Selected Seyfert 2 Galaxy IRAS 18325-5926: The X-Ray Source and Nuclear Obscuration

K. Iwasawa, H. Kunieda, Y. Tawara, H. Awaki, K. Koyama, T. Murayama, Y. Taniguchi

Abstract

We report x-ray and optical spectroscopic observations of an IRAS- selected Seyfert 2 galaxy IRAS 18325-5926. The first x-ray observation of this object was made using the Ginga LAC. The x-ray source is found to be highly variable on time scales of 10^3^-10^4^ s, similar to those of Seyfert 1 nuclei. The x-ray spectrum is well described by power-law continuum with a photon-index {GAMMA} ~ 2.2 modified by photoelectric absorption intrinsic to the source with N_H_ ~ 1.4 x 10^22^ cm^-2^ and a broad ({sigma} ~0.6 keV) iron K line. The corrected x-ray luminosity in the 2-10 keV band is L_X_ = 5.4 x 10^43^h^-2^_50_ ergs s^-1^. We obtained new optical spectra in red and blue bands, which show the strong emission lines of typical Seyfert 2s with a heavy reddening (A_v_ = 3.5 mag). A blue asymmetry is obvious in some strong emission lines and we can resolve narrow (FWHM ~ 450 km s^-1^) and slightly blueshifted (~160 km s^-1^) broad (FWHM = 1200 km s^-1^) components. The optical classification of Seyfert 2s can be explained in terms of nuclear obscuration which may occur in the form of a "global" covering rather than in the form of a torus inferred from the unified model, since the extinction derived from optical and x-ray data are comparable. This fact suggests that the hypothesis in which the classification between Seyfert 1's and 2's depends on the orientation is not complete, and a global obscuration is likely to dominate the dusty IRAS galaxies with Seyfert 2 characteristics.

 
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