Induced magnetic field in accretion disks around neutron stars

Abstract

There are X-ray pulsating sources that are explained by accretion from disks around neutron stars. Such disks deserve a detailed analysis. In particular, the dipole magnetic field of the central star may penetrate the disk, giving rise to an induced magnetic field inside the disk due to the frozen-in condition. The growth of the induced field can be limited by the turbulent diffusion. In the present work, I calculate the induced field in this case. The problem is reduced to the induction equation to which I have found an analytical solution describing radial and vertical structures of the induced field. The radial structure is close to the earlier predicted dependence on the difference in angular velocities between the magnetosphere and disk, $b \propto \Omega_{\rm s} - \Omega_{\rm k}$, while the vertical structure of an induced field is close to the linear dependence on the altitude above the equator, $b \propto z$. The possibility of the existence of non-stationary quasi-periodic components of the induced field is discussed.Comment: 8 pages, 3 figures, accepted to Astronomy Letters, proceedings of Physics of Neutron Stars conference (10-14 July 2023, Saint Petersburg, Russia), translation by the autho