General-Relativistic Neutron Star Magnetospheres

Jérôme Pétri, Observatoire astronomique de Strasbourg, France

Magnetic fields inside and around neutron stars are at the heart of pulsar magnetospheric activity. The variety of electromagnetic field topologies could lead to the observed diversity of neutron star classes. Thus it is important to include multipolar components to a presumably dominant dipolar magnetic field. Moreover, pulsar magnetospheres are shaped by ultra-relativistic electron/positron plasmas flowing in a strong magnetic field and subject to strong gravitational fields. The former induces magnetospheric currents and space charges responsible for the distortion of the electromagnetic field based on pure electrodynamics. The latter induces other perturbations in these fields based on space-time curvature. The force-free approximation describes the response of this magnetosphere to the presence of currents and charges and has been investigated by many authors. In this context, general relativity has been less discussed to quantify its influence on neutron star electrodynamics.

In this talk, we show computations of general-relativistic force-free pulsar magnetospheres for realistic magnetic field configurations such as the inclined dipole. We perform time-dependent simulations of Maxwell equations in the 3+1 formalism of a stationary background metric in the slow-rotation approximation. Multipolar fields in a strong gravity regime are also investigated. Approximate formulas for the electromagnetic field including frame dragging are computed from which the Poynting flux and the braking index are estimated. Both analytical and numerical tools are employed.