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Title:
ASCA PV observations of the Seyfert 2 galaxy NGC 4388: the obscured nucleus and its X-ray emission
Authors:
Iwasawa, K.; Fabian, A. C.; Ueno, S.; Awaki, H.; Fukazawa, Y.; Matsushita, K.; Makishima, K.
Affiliation:
AA(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA), AB(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA), AC(Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan), AD(Department of Physics, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan), AE(Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan), AF(Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan), AG(Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 285, Issue 4, pp. 683-692. (MNRAS Homepage)
Publication Date:
03/1997
Origin:
MNRAS
MNRAS Keywords:
GALAXIES: ACTIVE, GALAXIES: INDIVIDUAL: NGC 4388, GALAXIES: SEYFERT, X-RAYS: GALAXIES
Bibliographic Code:
1997MNRAS.285..683I

Abstract

We present results on the Seyfert 2 galaxy NGC 4388 in the Virgo cluster observed with ASCA during its performance verification (PV) phase. The 0.5-10 keV X-ray spectrum consists of multiple components: (1) a continuum component heavily absorbed by a column density N_H~4x10^23cm^-2 above 3 keV; (2) a strong 6.4-keV line (equivalent width EW~500eV) (3) a weak flat continuum between 1 and 3 keV; and (4) excess soft X-ray emission below 1 keV. The detection of strong absorption for the hard X-ray component is firm evidence for an obscured active nucleus in this Seyfert 2 galaxy. The absorption-corrected X-ray luminosity is about 2x10^42erg s^-1. This is the first time that the fluorescent iron K line has been detected in this object; the large EW is a common property of classical Seyfert 2 nuclei. The flat spectrum in the intermediate energy range may be a scattered continuum from the central source. The soft X-ray emission below 1 keV can be thermal emission from a temperature kT~=0.5keV, consistent with the spatially extended emission observed by ROSAT HRI. However, the low abundance (Z~0.05Z_solar) and high mass flow rate required for the thermal model and an iron K line stronger than expected from the obscuring torus model are puzzling. An alternative consistent solution can be obtained if the central source was a hundred times more luminous over a thousand years ago. All the X-ray emission below 3 keV is then scattered radiation.

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