Spin Period Evolution of Recycled Pulsar in Accreting Binary

TL;DR

This study models the spin-period evolution of recycled pulsars in binary systems, considering magnetic field decay and accretion effects, to explain the observed maximum spin frequencies of millisecond pulsars.

Contribution

It introduces a comprehensive model that accounts for accretion-induced magnetic decay and torque effects, explaining the minimum spin period and maximum spin frequency of MSPs.

Findings

Minimum spin period is independent of initial conditions when accreting >0.2 solar masses.

Fastest MSP spin frequency (~716 Hz) linked to a critical fastness parameter of 0.55.

Gravitational wave torque and accretion torque influence the spin evolution.

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, respectively. The results indicate that the minimum spin-period (or maximum spin frequency) of millisecond pulsar (MSP) is independent of the initial conditions and accretion rate when the neutron star (NS) accretes $\sim> 0.2\ms$. 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 about $\omega_{c}=0.55$. Furthermore, the comparisons with the observational data are presented in the field-period ($B-P$) diagram.