General relativistic activation of the polar cap of compact neutron stars

Magnetospheres of compact objects such as neutron stars and black holes are complex systems where quantum electrodynamic (QED) processes, kinetic-scale pair plasma physics and general relativity (GR) play all an important role. To study such intricate and exotic systems, advanced simulation techniques are required. In this work, we try to understand under which conditions the pulsar mechanism is possible. Previous works have shown that it is the appearance of a spacelike region on the polar cap, induced by the frame-dragging effect, that triggers this mechanism for low obliquity rotators [e.g. A.Philippov et al ApJ 2015 and S.Gralla et al ApJ 2016]. However, these works were either fluid models or neglected the GR effects on particle dynamics. Making use of a recently developed GR module for the particle-in-cell (PIC) code OSIRIS, we study the least favorable configuration, the aligned rotator, employing the slow rotation limit of the Kerr metric. We show that indeed it is possible to ignite the polar cap if GR effects are included. In addition, we demonstrate that the pulsar mechanism can only exist for stars with a Schwarzschild radius larger than 0.45 stellar radii. Finally, we characterize the new spacelike region and compare it to previous force-free models.