  Recent X-ray observations have shown evidence for exceptionally broad and
skewed iron K alpha emission lines from several accreting black hole systems.
The lines are assumed to be due to fluorescence of the accretion disk
illuminated by a surrounding corona and require a steep emissivity profile
increasing in to the innermost radius. This appears to question both standard
accretion disc theory and the zero torque assumption for the inner boundary
condition, both of which predict a much less extreme profile. Instead it argues
that a torque may be present due to magnetic coupling with matter in the
plunging region or even to the spinning black hole itself. Discussion so far
has centered on the torque acting on the disc. However the crucial determinant
of the iron line profile is the radial variation of the power radiated in the
corona. Here we study the effects of different inner boundary conditions on the
coronal emissivity and on the profiles of the observable Fe K alpha lines. We
argue that in the extreme case where a prominent highly redshifted component of
the iron line is detected, requiring a steep emissivity profile in the
innermost part and a flatter one outside, energy from the gas plunging into the
black hole is being fed directly to the corona.
