  The colossal power output of active galactic nuclei (AGN) is believed to be
fueled by the accretion of matter onto a supermassive black hole. This central
accreting region of AGN has hitherto been spatially unresolved and its
structure therefore unknown. Here we propose that a previously reported `deep
minimum' in the X-ray intensity of the AGN MCG-6-30-15, was due to a unique
X-ray occultation event and that it probes structure of the central engine on
scales < 1e14 cm, or 1.4e-7 arcseconds. The data are consistent with a bright
central source surrounded by a less intense ring, which we identify with the
inner edge of an accretion disk. These may be the first direct measurements of
the spatial structure and geometry of the accreting black-hole system in an
active galaxy.If the ring of X-ray emission is identified with the inner edge
of an accretion disk, upper limits on the BH mass can be derived. Our
occultation interpretation is controversial in the sense that X-ray variability
in AGNs is normally attributed to intrinsic physical changes in the X-ray
emission region, such as disk or coronal instabilities.
