From March 06, 2019 13:15 until March 06, 2019 13:45
At Seminar Room
We consider the equilibrium structures of magnetar magnetospheres, given through numerical solutions of the force-free Grad-Shafranov equation. We find that in certain cases multiple solutions can be constructed, where the solutions with lower energies likely represent the stable configurations. We then consider the long-term magnetic field evolution in the stellar interior coupled to an external force-free magnetosphere. As a generalization of the usual vacuum boundary conditions, this model allows for currents to flow into and out of the magnetosphere. We find that on timescales of the order of kyr, the energy stored in the magnetosphere increases until a critical point is reached beyond which force-free equilibria are not possible. We argue that at this point some large-scale reorganization of the magnetic field structure must take place, releasing part of the stored energy. The energy budget available for such events is consistent with observations of magnetars.