Coupled polar–axial magnetar oscillations

We study coupled axial and polar axisymmetric oscillations of a neutron star endowed with a strong magnetic field, having both poloidal and toroidal components. The toroidal component of the magnetic field is driving the coupling between the polar and axial oscillations. The star is composed of a fluid core as well as a solid crust. Using a two-dimensional general relativistic simulation and a magnetic field B= 1016 G, we study the change in the polar and axial spectrum caused by the coupling. We find that the axial spectrum suffers a dramatic change in its nature, losing its continuum character. In fact, we find that only the ‘edges’ of the continua survive, generating a discrete spectrum. As a consequence the crustal frequencies, which in our previous simulation could be absorbed by the continua, if they were embedded inside it, are now long-living oscillations. They may lose their energy only in the very special case that they are in resonance with the ‘edges’ of the continua.