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

Abstract

Recent observations have shown that the Fe Kalpha line profile of the Seyfert~1 galaxy MCG-06-30-15 is strongly variable. We attempt accretion disk model fits to the Fa Kalpha line profiles in a high, low and medium continuum luminosity phase of this source. During the monitoring by Iwasawa et al. (1996) a broad red-shifted component remained reasonably constant while a narrower component at $\approx$ 6.4 keV strongly responded to continuum changes. Physically consistent fits are possible if the index xi of the power-law emissivity 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 disk model interpretation. We suggest that the actual shape may be a broad redshifted Gaussian. Three lines of evidence support the interpretation of the Fe Kalpha line as multicomponent, beyond the lack of correlation in the response 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 keV is inconsistent with expectations of a random distribution of disk orientations. (2) The average Fe Kalpha profile for a sample of 16 mostly Seyfert~1's suggests a natural decomposition into two Gaussians one unshifted/narrow and the other redshifted/broad. (3) Evidence for emission in excess to the expectation of disk models on the high energy side of the Fe Kalpha profile is both a challenge for low inclination disk models and support for the two component decomposition.