  X-ray observations with Chandra and XMM-Newton have shown that there are
relatively narrow cores to the iron K-alpha emission lines in active galactic
nuclei (AGN). Plausible origins for this core emission include the outer
regions of an accretion disk, a pc-scale molecular torus, and the optical
broad-line region (BLR). Using data from the literature it is shown that no
correlation exists between the Fe K-alpha core width and the BLR (specifically
H-beta) line width. This shows that in general the iron K-alpha core emission
does not arise from the BLR. There is a similar lack of correlation between the
width of the Fe K-alpha core and black hole mass. The average K-alpha width is
about a factor of two lower than the H-beta width. It therefore seems likely
that in many cases the narrow core arises in the torus. There is a very wide
range of observed Fe K-alpha core widths, however, and this argues for multiple
origins. The simplest explanation for the observed line profiles in AGN is that
they are due to a mixing of very narrow emission from the inner edge of the
torus, and broadened emission from the accretion disk, in varying proportions
from object-to-object.
