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

Open Access
Publisher Website
Google Scholar
Abstract
Recent observations have shown that the Fe Kα line profile of the Seyfert 1 galaxy MCG -06-30-15 is strongly variable. We attempt accretion disk model fits to the Fe Kα line profiles in high, low, and medium continuum luminosity phases of this source. During the monitoring by Iwasawa et al., a broad redshifted component remained reasonably constant, while a narrower component at ≈ 6.4 keV responded strongly to continuum changes. Physically consistent fits are possible if the index ξ of the power-law emissivity changes from 0.7 (high phase) to 3.0 (low phase). The shape of the redshifted component at the 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 Kα line as consisting of multiple components, 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 Kα profile for a sample of 16 mostly Seyfert 1 galaxies suggests a natural decomposition into two Gaussians: one is unshifted/narrow, and the other is redshifted/broad. (3) Evidence for emission in excess of the expectation of disk models on the high-energy side of the Fe Kα profile is both a challenge for low-inclination disk models and support for the two-component decomposition.
All Related Versions