We present an analysis of the Vela X-1's "off-states" based on Suzaku
observations taken in June 2008. Defined as states in which the flux sudden
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. Eventually, we discuss
our findings in 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).Comment: 4 pages 4 figures; accepted for publication in A&A letters
(20/02/2011); v1.1 - some changes in language + added 3 reference
