Disk Models for MCG −06-30-15: The Variability Challenge

Recent observations have shown that the Fe Kalpha line profile of theSeyfert~1 galaxy MCG-06-30-15 is strongly variable. We attempt accretion diskmodel fits to the Fa Kalpha line profiles in a high, low and medium continuumluminosity phase of this source. During the monitoring by Iwasawa et al. (1996)a broad red-shifted component remained reasonably constant while a narrowercomponent at $\approx$ 6.4 keV strongly responded to continuum changes.Physically consistent fits are possible if the index xi of the power-lawemissivity changes from 0.7 (high phase) to 3.0 (low phase). The shape of the red-shifted component at low phase is crucial to the diskmodel interpretation. We suggest that the actual shape may be a broadredshifted Gaussian. Three lines of evidence support the interpretation of theFe Kalpha line as multicomponent, beyond the lack of correlation in theresponse to continuum changes of the red and blue components in MCG -06-30-15.(1) We show that the strong concentration of narrow peak centroids at 6.4 keVis inconsistent with expectations of a random distribution of diskorientations. (2) The average Fe Kalpha profile for a sample of 16 mostlySeyfert~1's suggests a natural decomposition into two Gaussians oneunshifted/narrow and the other redshifted/broad. (3) Evidence for emission inexcess to the expectation of disk models on the high energy side of the FeKalpha profile is both a challenge for low inclination disk models and supportfor the two component decomposition.Comment: 2 Figures, 1 table. Padova preprin