1997A&A...320..840C

We discuss serendipitous ROSAT observations of the Be transient A0538-66, which contains the fastest known accreting X-ray pulsar (69ms). We show that this transient is detected several times during quiescence at a level of about 10^34–35erg/s. Considering this low luminosity it is more likely that X-rays are produced by matter falling onto the neutron star magnetosphere, rather than onto the star surface. This could be the first example of an X-ray source in the "propeller regime".