  We report on the variability of the iron K emission line in the Seyfert 1
galaxy MCG--6-30-15 during a four-day ASCA observation. The line consists of a
narrow core at an energy of about 6.4 keV, and a broad red wing extending to
below 5 keV, which are interpreted as line emission arising from the inner
parts of an accretion disk. The narrow core correlates well with the continuum
flux whereas the broad wing weakly anti-correlates. When the source is
brightest, the line is dominated by the narrow core, whilst during a deep
minimum, the narrow core is very weak and a huge red tail appears. However, at
other times when the continuum shows rather rapid changes, the broad wing is
more variable than the narrow core, and shows evidence for correlated changes
contrary to its long time scale behaviour. The peculiar line profile during the
deep minimum spectrum suggests that the line emitting region is very close to a
central spinning (Kerr) black hole where enormous gravitational effects
operate.
