Criteria for identification of subsonic propellers

The state of a subsonic propeller in the evolutionary tracks of magnetized compact stars is intermediate between the states of a supersonic propeller and an accretor. We show that neutron stars in this state would manifest themselves as accretion-powered pulsars of low (or moderate) luminosity. The criteria that allow subsonic propellers to be distinguished from accretors include a soft X-ray spectrum, a limited range of admissible spin periods, and a rapid spindown.