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L.W. Brenneman, C.S. Reynolds (U. Maryland, College Park)
Because black holes cannot be observed directly, what we know of the spacetime immediately surrounding the event horizon must be gleaned through indirect methods. One of the most telling diagnostic tools currently employed for this purpose is the observation of relativistically broadened X-ray spectral lines emitted from the inner regions of the accretion disk surrounding the black hole. By fitting the data with established models, we can obtain best-fit values for the parameters governing the line broadening mechanisms. In particular, evaluating the angular momentum of a black hole against its other environmental parameters could provide valuable information about the nature of the accretion mechanism, as well as the structure and evolution of the black hole/accretion disk system.
The publicly available models currently being used for such fits have become out of date to the point where they are inadequate for modeling high-quality data from observatories such as Chandra and XMM-Newton. I have revised these existing models to speed up the run time of the code and have added a free parameter describing black hole spin. The new model, known as {\tt kerrdisk}, is currently being applied to a sample of very high signal-to-noise XMM and Chandra data. Herein I present the fitting results for the canonical Seyfert-1 galaxy MCG--6-30-15, thought to harbor a black hole of near-maximal spin based on the observed breadth of the Fe-K line emitted from its disk. Above 2 keV the system is very accurately described by a power law continuum, a narrow cold iron line at 6.4 keV, a narrow ionized H-like iron line at 6.9 keV, and a highly broadened iron line centered at ~6.5 keV with a spin parameter of a > 0.9.
We gratefully acknowledge funding from NSF grant AST0205990, which has contributed to this research.
Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.