Investigation On The Spin Evolution Of Young Neutron Stars

In this thesis we investigate the spin evolution of young neutron stars. Ac-cretion and magnetic field evolution play an important role in the spin evolution of neutron stars, and we explore the influence of these two factors on the spin evolution of neutron stars. The structure of the thesis is organized as follows:In chapter1, we first briefly introduce the discovery of neutron stars, then describe the characteristics of different types of neutron stars. Finally, we review the mechanisms and models of the spin evolution of neutron stars.In chapter2, we explore the possible evolutionary tracks of the neutron star in the transient Be/X-ray binary SXP1062discovered recently. The most outstanding feature of this source is its association with a10-40kyr young shell-like supernova remnant. The spin period of this pulsar is quitely long～1062s, with an extraordinarily large period derivative. An effective spin-down mechanism is required to explain its long spin period which seems to be in conflict with its young age. Here we adopt different initial parameters and spin-down mechanisms to calculate the possible evolutionary tracks of this source. Our results strongly suggest that the binary harbors or harbored a magnetar.In chapter3, we study the spin evolution of young isolated neutron stars. The observed braking indices of young isolated neutron stars are all incompatible with the classical model in which the spin evolution is dominated by magneto-dipole radiation with a constant magnetic field. Assuming that the neutron magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we develop a model taking into account both fallback accretion and magnetic field evolution, and carry out Monte-Carlo simulation of the spin evolution of young neutron stars with different initial parameters. The calculated braking indices mostly range from-1to3, which is compatible with observations. We also compare the characteristic age and the true age of puslars. In order to compare with observations we choose the pulsars associted with supernova remnants and use the ages of the supernova remnants as the true ages of the pulsars. Our results suggest that the initial spin periods of neutron stars might occupy a relatively wide range.Chapter4is the summary and prospects of our works.