Understanding the coexistence of spin-up and spin-down behaviors in long period X-ray pulsars

Abstract

Assuming the wind-fed accretion magnetars in long period X-ray pulsars, we calculated the rotational evolution of the neutron stars. Our calculations considered the effects of the magnetic field decay in magnetars. The results show that wind-fed accretion magnetars can evolve to the long period X-ray pulsars with a spin period much longer than 1000 s. The spin-down trend observed in 4U 2206+54 like sources is expected when the young X-ray binary systems are on the way to their equilibrium period. Detailed calculations showed that its spin-down may be affected by accretion with outflows or accretion while spin-down. Due to the magnetic field decay in magnetars, wind-fed accretion magnetars will have a decreasing equilibrium period for a constant mass accretion rate. For 2S 0114+65, the spin-up rate due to magnetic field decay is one order of magnitude smaller than the observations. The spin-up rate of 2S 0114+65 may be attributed to the formation of a transient disk during wind accretion. The slowest X-ray pulsar AX J1910.7+0917 would be a link source between 4U 2206+54 and 2S 0114+65.

9 pages, 5 figures, to be published in MNRAS

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• Superorbital Modulation in the High-Mass X-ray Binary 4U 1538-52, and Possible Modulation in IGR J16393-4643
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• SALT observations of the supernova remnant MCSNR J0127-7332 and its associated Be X-ray binary SXP 1062 in the SMC
• Spin evolution of neutron stars in wind-fed high mass X-ray binaries
• X-Ray Views of Galactic Accreting Pulsars in High-Mass X-Ray Binaries
• SALT spectroscopy of the HMXB associated with the LMC supernova remnant MCSNR\,J0513$-$6724
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