2011A&A...529A..52D

We present an analysis of the Vela X-1 ``off-states'' based on Suzaku observations taken in June 2008. Defined as states in which the flux suddenly decreases below the instrumental sensitivity, these ``off-states'' have been interpreted by several authors as the onset of the ``propeller regime''. For the first time ever, however, we find that the source does not turn off and, although the flux drops by a factor of 20 during the three recorded ``off-states'', pulsations are still observed. The spectrum and the pulse profiles of the ``off-states'' are also presented. We discuss our findings in the framework of the ``gated accretion'' scenario and conclude that most likely the residual flux is due to the accretion of matter leaking through the magnetosphere by means of Kelvin-Helmholz instabilities (KHI).