A particle simulation for the global pulsar magnetosphere: the pulsar wind linked to the outer gaps

Abstract

Soon after the discovery of radio pulsars in 1967, the pulsars are identified as strongly magnetic (typically 10 12 G) rapidly rotating (∼10 2 - 0.1 Hz) neutron stars. However, the mechanism of particle acceleration in the pulsar magnetosphere has been a longstanding problem. The central problem is why the rotation power manifests itself in both gamma-ray beams and a highly relativistic wind of electron-positron plasmas, which excites surrounding nebulae observed in X-ray. Here we show with a three-dimensional particle simulation for the global axisymmetric magnetosphere that a steady outflow of electron-positron pairs is formed with associated pair sources, which are the gamma-ray emitting regions within the light cylinder. The magnetic field is assumed to be a dipole, and to be consistent, the pair creation rate is taken to be small, so that the model might be applicable to old pulsars such as Geminga. The pair sources are charge-deficient regions around the null surface, and we identify them as the outer gap. The wind mechanism is the electromagnetic induction which brings about fast azimuthal motion and eventually trans-field drift by radiation drag in the close vicinity of the light cylinder and beyond. The wind causes loss of particles from the system. This maintains charge deficiency in the outer gap and pair creation. The model is thus in a steady state, balancing loss and supply of particles. Our simulation implies how the wind coexists with the gamma-ray emitting regions in the pulsar magnetosphere.