Three-dimensional numerical simulations of the pulsar magentoshere: Preliminary results

We investigate the three-dimensional structure of the pulsar magnetosphere through time-dependent numerical simulations of a magnetic dipole that is set in rotation. We developed our own Eulerian finite difference time domain numerical solver of force-free electrodynamics and implemented the technique of non-reflecting and absorbing outer boundaries. This allows us to run our simulations for many stellar rotations, and thus claim with confidence that we have reached a steady state. A quasi-stationary corotating pattern is established, in agreement with previous numerical solutions. We discuss the prospects of our code for future high-resolution investigations of dissipation, particle acceleration, and temporal variability.Comment: 9 pages, 4 figures. Astronomy & Astrophysics, in pres

MeV Pulsars: Modeling Spectra and Polarization

A sub-population of energetic rotation-powered pulsars show high fluxes of pulsed non-thermal hard X-ray emission. While this MeV pulsar population includes some radio-loud pulsars like the Crab, a significant number have no detected radio or GeV emission, a mystery since gamma- ray emission is a common characteristic of pulsars with high spin-down power. Their steeply rising hard X-ray spectral energy distributions (SEDs) suggest peaks at 0.1 - 1 MeV but they have not been detected above 200 keV. Several upcoming and planned telescopes may shed light on the MeV pulsars. The Neutron star Interior Composition ExploreR (NICER) will observe pulsars in the 0.2 - 12 keV band and may discover additional MeV pulsars. Planned telescopes, such as All-Sky Medium-Energy Gamma-Ray Observatory (AMEGO) and e-ASTROGAM, will detect emission above 0.2 MeV and polarization in the 0.2 - 10 MeV band. We present a model for the spectrum and polarization of MeV pulsars where the X-ray emission comes from electron- positron pairs radiating in the outer magnetosphere and current sheet. This model predicts that the peak of the SED increases with surface magnetic field strength if the pairs are produced in polar cap cascades. For small inclination angles, a range of viewing angles can miss both the radio pulse and the GeV pulse from particles accelerating near the current sheet. Characterizing the emission and geometry of MeV pulsars can thus provide clues to the source of pairs and acceleration in the magnetosphere.Comment: 8 pages, 5 figures, published in Proceedings of Scienc

The Extended Pulsar Magnetosphere

We present the structure of the 3D ideal MHD pulsar magnetosphere to a radius ten times that of the light cylinder, a distance about an order of magnitude larger than any previous such numerical treatment. Its overall structure exhibits a stable, smooth, well-defined undulating current sheet which approaches the kinematic split monopole solution of Bogovalov 1999 only after a careful introduction of diffusivity even in the highest resolution simulations. It also exhibits an intriguing spiral region at the crossing of two zero charge surfaces on the current sheet, which shows a destabilizing behavior more prominent in higher resolution simulations. We discuss the possibility that this region is physically (and not numerically) unstable. Finally, we present the spiral pulsar antenna radiation pattern