A case study of MCG-6-30-15

There are a small number of AGN that have become test-beds for the use of X-ray observations to probe black hole and accretion disk physics. Here, we shall describe studies of one such object -- the Seyfert 1 galaxy MCG-6-30-15. This is a somewhat unremarkable S0-type galaxy in the constellation of Centaurus, with a redshift of $z=0.008$, placing it at a distance of $D=37{\rm\thinspace Mpc}$. As we will describe, X-ray studies of this object have allowed us access to some of the most exotic black hole physics yet observed.

Unfortunately, the mass of the supermassive black hole in this AGN remains rather poorly determined -- some general arguments place it in the range $10^6-2\times 10^7\hbox{$\rm\thinspace M_{\odot}$}$[203]. Most of the astrophysical conclusions drawn below are robust to this uncertainty since, to first order, the mass of the black hole merely scales the size of the system rather than changing any of the underlying physics. However, constraints on the mass are important if we are to physically interpret observed temporal variability, since all of the fundamental time scales of the accretion disk scale linearly with black hole mass.