100$ days, see @wij01). Thanks to the good sensitivity of the [[*XMM*]{}-Newton]{} and [[*Swift*]{}-XRT]{} satellite, @wij03 and @cam08 measured a minimum luminosity of $\sim5\times10^{32}\rm\,erg\,s^{-1}$ between the flares in the re-flaring state in the 2000 and 2005 outburst (assuming a distance of 3.5 kpc). In 2002 [@wij04] and 2008 [@har09] the re-flaring state was observed with [[*RXTE*]{}]{} for approximately 1 month.

@cam08 interpreted the observed low luminosities as a signature of the onset of the propeller regime. The propeller regime is characterized by a Keplerian velocity in the innermost region of the accretion disk that is slower than the rotational velocity of the neutron star magnetosphere. In its original formulation [@ill75] it was proposed to suppress the accretion flow onto the neutron star surface. The gas, carrying part of the neutron star angular momentum, was thought to be expelled and spin down the neutron star. @gho79a [@gho79b] proposed that spin down and accretion could occur simultaneously and recent MHD simulations (@rom05, @ust06) show that two different propeller regimes are possible: a strong propeller, characterized by a strong outflow of gas, and a weak propeller, with no outflows. In both cases a magnetically channeled accretion flow onto the neutron star surface is 