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

Abstract

We present results from fitting of ionized accretion disc models to three long ASCA observations of the Seyfert 1 galaxy MCG-6-30-15. All three data sets can be fitted by a model consisting of ionized reflection from the inner region of the accretion disc (with twice solar Fe abundance) and a separate disc-line component from farther out on the disc. The disc-line is required to fit the height of the observed Fe Kα 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 Kα line at 6.4 keV is required to fit the observed line. The ionized disc models predict that O viii Kα, C vi Kα, Fe xvii Lα and Fe xviii Lα lines will appear in the soft X-ray region of the reflection spectrum, but are greatly blurred as a result of Compton scattering. The equivalent width (EW) of O viii Kα 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 cannot 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 Kα 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.