Axisymmetric force-free magnetospheres and theoretical models beyond general relativity: Magnetic moment of axion stars

Abstract

Abstract: The magnetosphere structure of a magnetar is considered in the context of a theory of gravity with dynamical torsion field beyond the standard General Relativity (GR) with the purpose of determining in a theoretical way the corresponding electromagnetic fields of the compact star, as well as being able to express phenomenologically the magnetic moment of an axion star. To this end, the axially symmetric version of the Grad–Shafranov equation (GSE) is obtained in this theoretical framework where the resulting GSE solution in the case of the magnetosphere corresponds to a stream function containing also a pseudoscalar part. As we shown before, this function solution under axisymmetry presents a complex character that could be associated with an axidilaton.