On the hysteresis effect in transitions between accretion and propeller regimes

On the hysteresis effect in transitions between accretion and propeller regimes by Sercan Çıkıntoğlu et al. on Wednesday 23 November Some observations and numerical simulations of disc-magnetosphere interaction show that accretion can proceed in the propeller regime. When the Alfv\'en radius is beyond the corotation radius, matter climbs up to the high latitudes where the Alfv\'en surface is inside the equilibrium surface and can accrete. We calculate the fraction of the mass flux in the disc that can accrete onto the neutron star depending on the fastness parameter and the inclination angle between rotation and magnetic axis. We find that, for a narrow range of the fastness parameter, the Alfv\'en and the equilibrium surfaces intersect at two different critical latitudes. While the system is transiting from the propeller to the accretion regime (the initial rise of an outburst), accretion proceeds from the region above the higher critical latitude. In transitions from the accretion to the propeller regime (decay of the outburst), accretion of matter can proceed from the disc midplane. As a result, the transition from the propeller to the accretion regime occurs at a luminosity higher than the transition from the accretion to the propeller regime. We discuss the implications of our results for spectral transitions exhibited by low-mass X-ray binaries. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.12945v1