Ab-initio Pulsar Magnetosphere: Particle Acceleration in Oblique Rotators and High-energy Emission Modeling

• Published in: The Astrophysical journal 2018-03, Vol.855 (2), p.94
• Main Authors: Philippov, Alexander A., Spitkovsky, Anatoly
• Format: Article
• Language: English
• Subjects: Activation; Astrophysics; Computer simulation; Cosmic rays; Current sheets; Energy flux; Equatorial currents; Gamma rays; High energy astronomy; Inclination; Ion extraction; Light curve; Line voltage; Magnetic reconnection; Pair production; Particle acceleration; Particle energy; Particle in cell technique; Photon emission; Plasma density; plasmas; Pulsar magnetospheres; Pulsar winds; Pulsars; pulsars: general; Radiation; Relativity; stars: magnetic field; stars: rotation; Stellar surfaces; Stellar winds
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aaabbc

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, the effects of general relativity increase the fraction of the open field lines that support active pair discharge. We find that the plasma density and particle energy flux in the pulsar wind are highly non-uniform with latitude. A 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, the calculated light curves contain two strong peaks, which is in general agreement with Fermi observations. The radiative efficiency decreases with increasing pulsar inclination and increasing efficiency of pair production in the current sheet, which explains the observed scatter in Lγ versus . 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.