Using a stationary slab model, we have shown that relative disk/source
motion can significantly affect (and usually enhance) the EW of the
fluorescent iron K 
line. This mechanism might be responsible for
producing the strong iron lines seen in many AGN. Viable alternative
explanations require a rather large iron overabundance, or invoke some
geometry in which the disk subtends more than 
sr as seen by the
X-ray source.
As is intuitively clear, the SR enhancement of the line EW is especially important if the X-ray emitting material is moving directly towards the disk. This is exactly the flow pattern envisaged in the magnetized accretion disk model of FR93. By analogy with solar flares, they argue that the corona is magnetically confined by loops of magnetic field which have footpoints in the accretion disk. They suggest two processes that might leads to significant material motion. Firstly, if the footpoints of the loops are forced (by motions in the disk) into a configuration whose topology permits a lower energy magnetic field structure, the coronal loop structure may become unstable, leading to the release of magnetic field energy into bulk kinetic energy of the plasma. Coronal shock waves will result. Secondly, the disk motion may force loops of opposite polarity together, thereby resulting in magnetic reconnection. This would also channel a substantial amount of energy into particle energy. Since these phenomena are likely to occur predominately near the tops of the coronal loops (Field & Rogers 1992), the streaming of accelerated particles along the field lines will result in downwards motion of X-ray emitting material. FR93 use the subsequent beaming of the emission to channel much of the coronal energy back into the accretion disk (which is eventually lost as optical/UV thermal emission from the disk surface).
In the very near future, observations will begin to address the origin of
the strong iron lines. Very broad band X-ray observations (with RXTE
or Beppo-SAX, for example) will allow the iron line, iron edge and
Compton backscattered continuum to be simultaneously constrained. If the
iron lines are strong due to an iron-overabundance, this will be revealed
as an enhancement of the line relative to the Compton backscattered
continuum. On the other hand, if observations show both the iron line
and backscattered continuum to be enhanced above the predictions of the
`standard' model, then we must either consider a geometry in which the disk
subtends more than sr at the X-ray source, or invoke (special or
general) relativistic effects to enhance the overall X-ray reflection. It
is interesting to note that preliminary results for the Seyfert 1 galaxy
MCG-6-30-15 indicate that the backscattered continuum may somewhat
enhanced above the prediction of the standard model (Molendi et al. 1997),
although a self-consistent analysis, which includes the effects of iron
abundance on the shape of the backscattered continuum, still has to be
performed.
If it is confirmed that an overall enhancement of the X-ray reflection is required, the inclination dependence of the iron line properties will be important for disentangling the enhancement mechanisms. As shown in this work, if source motion is responsible for the enhancement, the EW of the line will decrease significantly as one considers sources at higher inclination (note that the inclination of the disk can be measured robustly from the iron line profile). This effect will be much stronger than the inclination dependence of the line just based on limb-darkening (George & Fabian 1991). A careful analysis of existing ASCA datasets might allow such a trend to be addressed.