The fact that the primary emission is beamed whereas the fluorescent
emission is not beamed has direct consequences for the observed EW of the
line. The relevant quantity is the ratio of the iron line flux to the
normalization of the observed primary continuum at the iron line energy.
Due to the effects of relativistic beaming, this primary flux normalization
is proportional to 
where, to recap, 
is the
angle between the source motion and the observers line of sight. Noting
that 
, the equivalent width of the iron line is given by
Figure 2: The enhancement in the iron line equivalent width W(v)/W(0) for
(a) downwards moving sources with velocity v, and (b) an ensemble of
sources moving with speed v (isotropically) parallel to the slab
plane. Four different inclinations are shown: 
(solid line),
(dashed line), 
(dotted line), and
(dot-dashed line).
Figure 2a shows the behaviour of W(v) for sources moving directly towards
the slab ( 
) for various inclinations of the observer i. It can
be seen that the SR beaming has a major effect on the EW of the iron line
for relatively small velocities, especially at low inclinations. The EWs
seen in Seyfert 1 nuclei (which have typical inclinations of 
) are often 2-3 times more than predicted by the standard model
(see Introduction). If all of this enhancement was due to SR effects
(rather than iron overabundance), we would require downwards motion at
. By contrast, Fig. 2b shows the behaviour of W(v) for
sources moving parallel to the plane of the slab ( 
). In
plotting these curves, it is assumed that there is an ensemble of such
sources with velocity vectors that are isotropically distributed in that
plane (i.e. we average over 
). Once this average is performed, the
resulting expression for the equivalent width is
It is seen from Fig. 2b that much higher source velocities are required to
produce a given enhancement in the iron line. To explain Seyfert 1 spectra
would require 
.