Dissipation, energy transfer, and spin-down luminosity in 2.5D PIC simulations of the pulsar magnetosphere

Abstract

We perform 2.5D axisymmetric simulations of the pulsar magnetosphere (aligned dipole rotator) using the charge conservative, relativistic, electromagnetic particle in cell code PICsar. Particle in cell codes are a powerful tool to use for studying the pulsar magnetosphere, because they can handle the force-free and vacuum limits and provide a self-consistent treatment of magnetic reconnection. In the limit of dense plasma throughout the magnetosphere, our solutions are everywhere in the force-free regime except for dissipative regions at the polar caps, in the current layers, and at the Y-point. These dissipative regions arise self-consistently, since we do not have any explicit dissipation in the code. A minimum of $ \approx 15-20\%$ of the electromagnetic spindown luminosity is transferred to the particles inside 5 light cylinder radii. However, the particles can carry as much as $\gtrsim 50 \%$ of the spindown luminosity if there is insufficient plasma in the outer magnetosphere to screen the component of electric field parallel to the magnetic field. In reality, the component of the spindown luminosity carried by the particles could be radiated as gamma rays, but high-frequency synchrotron emission would need to be implemented as a sub-grid process in our simulations and is not present for the current suite of runs. The value of the spindown luminosity in our simulations is within $\approx 10\%$ of the force-free value, and the structure of the electromagnetic fields in the magnetosphere is on the whole consistent with the force-free model.