"Magnetic gates" of accreting X-ray pulsars during giant outbursts

Abstract X-ray pulsars (XRPs) consist of a magnetized neutron star (NS) and an optical donor star. The NS accretes matter from the donor star, producing pulsed X-ray emission. In most cases the donor stars are Be stars, and accretion is episodic, that is, the NSs are generally X-ray dim, but occasionally experience outbursts. The triggering mechanism of giant outbursts remains mysterious. Here, we carry out a statistical study with the X-ray monitoring data, and obtain strong correlations between the spin periods of the NSs and the outburst parameters for the first time. We show that XRPs containing faster rotating NSs tend to display more violent eruptions. These results provide clear evidence of ``magnetic gates", that is, larger accretion rates are required to penetrate into a faster rotating magnetosphere.