X射线脉冲星周期的变化与吸积盘边界的K-H不稳定性

本文在中子星磁层与吸积盘之间引入了一个速度、密度、压强和磁场都连续变化的有限厚度的剪切层,以代替Anzer理论中的切向间断面,用磁流体力学方法讨论了中子星磁层与吸积盘交界处等离子体可压缩情况下平面波扰动的K-H不稳定性。结果表明,K-H不稳定性依然存在,径向波矢扰动成为不稳定的主要模式。文中特别讨论了剪切层厚度取值对中子星自转的影响,表明适当调节剪切层厚度就可解释X射线脉冲星周期的变化。将此模型应用到脉冲X射线源Her X-1上,得到较好的结果。

THE VARIATION OF PULSE PERIOD OF A X-RAY PULSAR AND K-H INSTABILITY AT THE BOUNDARY OF THE ACCRETION DISK

The boundary between the accretion disk and the magnetosphere of a neutron star is unstable. Instead of the approximation of a plane vortex sheet, this paper gives a new model. In the model the boundary is a sheared layer in which the velocity, density, pressure and magnetic field are distributed continuously. We present a study of the K-H instability in the layer. A dispersion equation is derived from the MHD equations for small perturbations about the equilibrium state of the compressible plasma. The study shows that the radial perturbations are the main factor in the mixture of the matter of the disk and the magnetic field. An investigation of the rotation period of the neutron star affected by the thickness of the layer is made. Applications of the model to the pulsating X-ray source Her X-1 give a better explanation of the observed variation of the pulse period.