Retrograde wind accretion – an alternative mechanism for long spin period of SFXTs
1 Institute of Astronomy, National Tsing Hua University, 30013 Hsinchu, Taiwan
2 Department of Physics, National Tsing Hua University, 30013 Hsinchu, Taiwan
Received: 10 July 2012
Accepted: 23 September 2012
A new class of high-mass X-ray binaries (HMXBs) – supergiant fast X-ray transients (SFXTs) – are discovered by INTEGRAL, which are associated with OB supergiants and present long spin periods. Observational evidence indicates that some accreting neutron stars in HMXBs display accretion reversals. It has been suggested that the inverted torque can lead to a very slow rotator. According to three characteristic radii in wind-fed accretion, we developed a retrograde accretion scenario and divided the accretion phase into three regimes, to interpret the formation of the long spin period of SFXTs. The accretion regime in some SFXT systems can be determined by their spin and orbital periods.
Key words: accretion, accretion disks / stars: neutron / X-rays: binaries
© ESO, 2012