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Title:
The iron K line complex in NGC1068: implications for X-ray reflection in the nucleus
Authors:
Iwasawa, K.; Fabian, A. C.; Matt, G.
Affiliation:
AA(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA), AB(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA), AC(Dipartimento di Fisica, Universita di Roma III, Via della Vasca Navale 84, I-00146 Roma, Italy)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 289, Issue 2, pp. 443-449. (MNRAS Homepage)
Publication Date:
08/1997
Origin:
MNRAS
MNRAS Keywords:
LINE: PROFILES, GALAXIES: ACTIVE, GALAXIES: INDIVIDUAL: NGC1068, X-RAYS: GALAXIES
Bibliographic Code:
1997MNRAS.289..443I

Abstract

We report a new analysis of ASCA data on the iron K line complex in NGC1068. The line complex basically consists of three components, as previously reported. A weak red wing of the 6.4-keV fluorescence iron K line is found. A plausible explanation is Compton scattering in optically thick, cold matter which can be identified with an obscuring torus or cold gas in the host galaxy. We also show that this `Compton shoulder' should be observable with ASCA using a simulated reflection spectrum. In order to explain the two higher energy lines as well as the cold 6.4-keV line, we fit the ASCA data with a composite model of cold and warm reflection. This shows that cold reflection dominates the observed X-ray emission above 4 keV; the estimated scattering fraction from the warm medium is found to be ~ 0.08 per cent, an order of magnitude below the standard value of 1 per cent obtained from previous observations in other wavebands. The two higher energy lines have large equivalent width (~ 3 keV) with respect to the warm-scattered continuum, suggesting that efficient resonant scattering operates. The line energies are systematically lower than those expected from resonant lines for FeXXV and FeXXVI by ~ 100 eV. The redshifts may be due to either the ionized gas of the warm mirror receding at a radial velocity of 4000-5000 km s^-1 or to effects of Compton scattering in a complicated geometry.

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