Relativistic ionized accretion disc models of MCG--6-30-15

Abstract

We present results from fitting ionized accretion disc models to three long ASCA observations of the Seyfert 1 galaxy MCG--6-30-15. All three datasets can be fit by a model consisting of ionized reflection from the inner region of the accretion disc (with twice solar Fe abundance) and a separate diskline component from farther out on the the disc. The diskline is required to fit the height of the observed Fe K line profile. However, we show that a much simpler model of reflection from a very weakly ionized constant density disc also fits the data. In this case only a single cold Fe K line at 6.4 keV is required to fit the observed line. The ionized disc models predict that O VIII K, C VI K, Fe XVII L, and Fe XVIII L lines will appear in the soft X-ray region of the reflection spectrum, but are greatly blurred due to Compton scattering. The equivalent width (EW) of O VIII K is estimated to be about 10 eV and seems to be as strong as the blend of the Fe L lines. This result creates difficulty for the claim of a strong relativistic O VIII line in the XMM-Newton grating spectrum of MCG--6-30-15, although we can not strictly rule it out since MCG--6-30-15 was in an anomalously low state during that observation. We find that increasing the O abundance or breaking the continuum below 2 keV will not significantly strengthen the line. The second Fe K line component in the ionized disc model may arise from neutral reflection from a flared disc, or from a second illumination event. The data cannot distinguish between the two cases, and we conclude that single zone ionized disc models have difficulty fitting these hard X-ray data of MCG--6-30-15.