  The physical conditions in the inner parsec of accretion disks believed to
orbit the central black holes in active galactic nuclei can be probed by
imaging the absorption of background radio emission by ionized gas in the disk.
We report high angular resolution observations of the nearby galaxy NGC 4261
which show evidence for free-free absorption by a thin, nearly edge-on disk at
several frequencies. The angular width, and probably the depth, of the
absorption appears to increase with decreasing frequency, as expected. Because
free-free absorption is much larger at lower frequencies, the longest possible
baselines are needed to provide adequate angular resolution; observing at
higher frequencies to improve resolution will not help.
