Estimation of Pulsar’s Initial Spin by the Magnetic Dipole Radiation and Wind Model

Abstract

The estimation of the initial spin period of pulsars involves the important questions such as the late stage evolution of massive stars and the formation process of neutron stars. However, the estimated initial spin exists the bias based on the magnetic dipole radiation (MDR) model, since the braking index of a dozen of observed pulsars ranges in \(1 < n < 3\) that is deviated from the expected value of 3 by MDR. The magnetic dipole radiation plus wind (MDRW) model for a pulsar successfully explains the evolution of the braking index between 1 and 3, by which we calculate the initial spins of the pulsars with the measured braking index, and obtain their distribution between \( \sim {\kern 1pt} 18\) and \( \sim {\kern 1pt} 50\) ms. This result is consistent with the statistics of the observed young pulsars, less than the fastest spin period of 16 ms of the rotation-powered X-ray pulsar PSR J0537–6910.