Ab-Initio Pulsar Magnetosphere: Particle acceleration in Oblique Rotators and High-energy Emission Modeling

Abstract

We perform global particle-in-cell simulations of pulsar magnetospheres including pair production, ion extraction from the surface, frame dragging corrections, and high energy photon emission and propagation. In the case of oblique rotators, effects of general relativity increase the fraction of open field lines which support active pair discharge. We find that the plasma density and particle energy flux in the pulsar wind are highly non-uniform with latitude. Significant fraction of the outgoing particle energy flux is carried by energetic ions, which are extracted from the stellar surface. Their energies may extend up to a large fraction of the open field line voltage, making them interesting candidates for ultra-high-energy cosmic rays. We show that pulsar gamma-ray radiation is dominated by synchrotron emission, produced by particles that are energized by relativistic magnetic reconnection close to the Y-point and in the equatorial current sheet. In most cases, calculated light curves contain two strong peaks, in general agreement with Fermi observations. The radiative efficiency decreases with increasing pulsar inclination and increasing efficiency of pair production in the current sheet, explaining the observed scatter in $L_{\gamma}$ vs $\dot{E}$. We find that the high-frequency cutoff in the spectra is regulated by the pair loading of the current sheet. Our findings lay the foundation for quantitative interpretation of Fermi observations of gamma-ray pulsars.