On the Bimodal Spin Period Distribution of Be/X-ray Pulsars

Abstract

It has been reported that there are two populations of Be/X-ray pulsars, with the pulse period distribution peaked at $\sim$ 10 s and $\sim$ 200 s, respectively. A possible explanation of this bimodal distribution is related to different accretion modes in Be/X-ray binaries. In this work, we investigate the spin evolution of Be/X-ray pulsars based on the magnetically threaded accretion disk model. Compared with previous works, we take into account several distinct and important factors of Be/X-ray binaries, including the transient accretion behavior and possible change of the accretion disk structure during quiescence. We demonstrate that current Be/X-ray pulsars are close to the spin equilibrium determined by the balance of spin-up during outbursts and spin-down during quiescence, and that the observed bimodal distribution can be well reproduced by the equilibrium spin periods with reasonable input parameters.

13 pages, 3 figures; accepted for publication in ApJ

References in corpus (5)

• The ultra luminous X-ray source NuSTAR J095551+6940.8: A magnetar in a high mass X-ray binary
• The origin of long-period X-ray pulsars
• On the Spin Period Distribution in Be/X-ray Binaries
• Spectral and temporal properties of RX J0520.5-6932 (LXP 8.04) during a type-I outburst
• Correlation between the luminosity and spin-period changes during outbursts of 12 Be binary pulsars observed by the MAXI/GSC and the Fermi/GBM

Cited by in corpus (3)

• Periodic Activities of Repeating Fast Radio Bursts from Be/X-ray Binary Systems
• Populations of evolved massive binary stars in the Small Magellanic Cloud I: Predictions from detailed evolution models
• Astrophysical parameters of LS 437 and the nature of X0726-260