Accretion magnetar in the close binary system 4U 2206+54

Abstract

The magneto-rotational evolution of a neutron star in the massive binary system 4U 2206+54 is discussed in light of the recent discovery of its 5555 s rotational period and its average rate of spin-down. We show that this behavior of the neutron star means that its magnetic field exceeds the quantum mechanical critical limit and it is an accretion magnetar. The system’s evolution is explained by wind driven mass transfer without formation of an accretion disk. The constant character of the x-ray source indicates a steady rate of accretion and raises anew the question of the stability of the boundary of the magnetosphere of a star undergoing spherical accretion. A solution to this problem is also a key to determining the mechanism for the slowing down of the star’s rotation.