Disk accretion onto magnetic neutron stars

The magnetic torque contributed by field-threading disk takes on a significant role in the total torque exerted on the magnetic neutron stars in X-ray binaries. In previous works, the toroidal field generated by rotational shear is estimated from the Faraday induction law. It is re-evaluated in this paper with the electrodynamical boundary conditions across the surface of the disk in an axisymmetric case. The dependence of the resistivity of disk plasma on radius is also estimated based on the standard disk theory. A more realistic expression of the disk torque is then derived. The applications to several disk-accreted X-ray pulsars are briefly discussed.Project supported by the National Nature Science Foundation of China and the funds from the State Education Commission for the training of Ph.D.'s