Spin period evolution of a recycled pulsar in an accreting binary

Abstract

We investigate the spin period evolutions of recycled pulsars in binary accreting systems. Taking both the accretion induced field decay and spin-up into consideration, we calculate their spin period evolutions influenced by the initial magnetic field strengths, initial spin periods, and accretion rates. The results indicate that the minimum spin period (or maximum spin frequency) of a millisecond pulsar (MSP) is independent of the initial conditions and accretion rate when the neutron star (NS) accretes the mass of ∼ 0.2 M⊙. The accretion torque with the fastness parameter and gravitational wave (GW) radiation torque may be responsible for the formation of the minimum spin period (maximum spin frequency). The fastest spin frequency (716 Hz) of MSP can be inferred to associate with a critical fastness parameter of about ωc = 0.55. Furthermore, comparisons with the observational data are presented in the field period (B-P) diagram. © 2011 ESO.