X-ray absorption lines suggest matter infalling onto the central black-hole of Mrk 509
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.