  Evidence for both red- and blue-shifted absorption lines due to ionized Fe in
the X-ray spectrum of the Seyfert 1 galaxy Mrk 509 are reported. These features
appear to be transient on time-scales as short as ~20 ks, and have been
observed with two different satellites, BeppoSAX and XMM-Newton. The red- and
blue-shifted lines are found at E~5.5 keV and ~8.1-8.3 keV (rest-frame),
respectively. The first is seen in one out of six BeppoSAX observations, the
latter is seen by both satellites. Under the assumption that the absorption is
due to either H- or He-like Iron, the implied velocities for the absorbing
matter are v~0.15-0.2 c, in both outward and inward directions. An alternative
explanation in terms of gravitational red-shift for the ~5.5 keV line cannot be
ruled out with the current data. We argue, however, that the temporal patterns
and sporadic nature of the lines are more easily reconciled with models which
predict important radial motions close to the central black hole, such as the
``aborted jet'' model, the ``thundercloud'' model, or magneto-hydrodynamical
models of jets and accretion-disks.
