Induced Magnetic Field in Accretion Disks Around Neutron Stars: Abstract and Introduction

Table of Links

Abstract and Introduction

Model of Disk and Neutron Star

Main Equations

The Solution for the Induced Field

Discussion

Conclusion and References

ABSTRACT

Keywords: neutron stars, accretion disks, magnetic field

DOI: ...

1. INTRODUCTION

The problem of the structure of an accretion disk interacting with the magnetic field of a central

star is closely related to X-ray sources with magnetized neutron stars (NSs). Modeling the disk, one needs to know the induced magnetic field inside and around the disk in order to properly account for the effects of the magnetic field. The situation when the NS magnetic field penetrates a disk is considered, the magnetic axis of the NS is inclined to the disk axis. Since the disk consists of ionized matter and the field lines are twisted by the movement of the disk, an induced field appears in the disk (Lai, 1999).

One of the first models of interaction between magnetic field and accretion disk was proposed by

Gosh and Lamb (Gosh et al., 1977; Gosh and Lamb, 1979a, b) to explain observed variations of NSs spin rates. They calculated the exchange of torque between the disk and the star through the magnetic field. At the time, their theoretical results were con- ∗E-mail: [email protected]

sistent with observations. However, these works introduced the induced field in a simplified way. Wang (1987) has demonstrated an inconsistency of the model of Gosh and Lamb. This problem motivated other authors to build more realistic models of the induced field.

The major points of the model presented below are as follows. In order to calculate the structure

of accretion disk, one needs to know both the radial and vertical structure of the induced magnetic field. In this work, the radial and vertical components of the induced field are separated. The magnetic diffusion coefficient varies with the radial coordinate in a physically plausible manner. The equation for the induced magnetic field is derived from the induction equation, and boundary conditions are set for this equation. The focus of this work is on the stationary axially symmetric induced magnetic field, although other possibilities are also discussed.