New Advances in the Modelling of Pulsar Magnetospheres

Abstract

The wealth of high-energy (E > 50 MeV) and very-high-energy (E > 100 GeV) data accumulated over the past few years have provided unprecedented opportunities to probe pulsar emission models. The Fermi Large Area Telescope (LAT) has now detected over 200 gamma-ray pulsars of vastly different ages, providing an extensive dataset of spectra and light curves compared to a mere decade ago. Ground-based Cherenkov telescopes deepened our appreciation of the mysterious richness of the pulsar mechanism by a surprise detection of pulsed emission up to 1 TeV from the Crab pulsar. These discoveries position us to make real progress in pulsar theory. A number of studies have developed new and enhanced existing dissipative magnetohydrodynamical (MHD) and particle-in-cell (PIC) codes to solve the global electrodynamics and pursue fundamental questions about magnetospheric particle injection, acceleration, and radiation. While MHD models capture the global aspects of pulsar magnetospheres, the microphysics need to be probed self-consistently by PIC simulations. Some dissipative MHD models consider the current sheet (CS) as an important site for high-energy curvature radiation (CR), while early PIC results point to energy dissipation taking place in the CS, where particles are accelerated by magnetic reconnection and may possibly emit $\gamma$ rays via synchrotron radiation (SR). This is in marked contrast to some older local emission models that studied CR $\gamma$ rays produced in gaps nearer to the spinning neutron star. The universality of these results should become clearer as current computational restrictions are overcome and boundary conditions are refined. Continued and combined polarimetric, spectral, and temporal measurements should aid us in scrutinising these new emission models in our persistent pursuit of a deeper understanding of the pulsar marvel.