The iron K line complex in NGC 1068: Implications for X-ray reflection in the nucleus

We report a new analysis of ASCA data on the iron K line complex in NGC 1068. The line complex basically consists of three components, as previously reported. A weak red wing of the 6.3-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 similar to 0.08 per cent, an order of magnitude below the standard value of I per cent obtained from previous observations in other wavebands. The two higher energy lines have large equivalent width (similar to 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 Fe XXV and Fe XXVI by similar to 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.