Accretion Phenomena at Neutron Stars
The basic picture of an X-ray pulsar is that of a strongly magnetized neutron star which accretes matter from its companion. The reason for mass transfer can be a strong wind of the companion or a Roche-lobe overflow from the companion through the inner Lagrangian point. In the latter case the matter forms an accretion disk around the neutron star, in which it spirals inwards and heats up due to viscous interaction. If the neutron star is strongly magnetized, the disk does not reach to the surface of the neutron star, because at the Alfven radius the matter is dominated by the magnetic forces. The physics of this region, where the matter couples to the magnetic field lines, is not yet fully understood. The ionized matter which is on the field lines is accelerated by the strong gravitational field and falls along the magnetic field lines towards the magnetic poles of the neutron star, where it reaches velocities of about c/2 (c = is the velocity of light). The fully ionized matter is stopped in the atmosphere of the neutron star and its kinetic energy is converted into radiation energy. This region, where the radiation is produced, is called the “hot spot”.
KeywordsNeutron Star Radiative Transfer Light Curve Magnetic Field Line Diffusion Approximation
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