Filling the Magnetospheres of Weak Pulsars

Abstract

Recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using Particle-in-Cell (PIC) techniques. These ab-initio simulations seem to indicate that pair creation through photon-photon collision at the light cylinder is required to sustain the pulsar engine. However, for many rotation-powered pulsars pair creation operates effectively only near the stellar surface where magnetic field is high. How these "weak pulsars" fill their magnetospheres without efficient photon-photon pair conversion in the outer magnetosphere is still an open question. In this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. When pair production is very efficient near the star, the pulsar magnetosphere converges to previously-reported solutions. However, in the intermediate regime where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with quasi-period about half of the rotation period. This new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core vs. conal emission patterns observed in pulsar radio signals.

A Numerical Model for the Multiwavelength Lightcurves of PSR J0030+0451

“…The global magnetosphere also remains dipole-like, but the magnetospheric current is redirected to modified polar caps due to the presence of higher multipole fields, in agreement with the prediction by Gralla et al (2017). Note that we did not include general relativistic corrections to ρ GJ , which will likely reduce ρ GJ and enhance j B /cρ GJ Chen et al 2020).…”

Radiative pulsar magnetospheres: oblique rotators

“…The connection between dissipation layers and radiation zones has been confirmed by kinetic simulations such as Philippov & Spitkovsky (2018) and Chen et al (2020).…”

“…The particle production assumption, either from the surface or from the lightcylinder or from the whole magnetosphere volume decides what on the global solution found in numerical simulations. Chen et al (2020) presented simulations not requiring efficient pair production in the vicinity of the light cylinder and found quasi-periodic solution able to explain the cone versus and core emission characteristics of radio pulses. Previously Chen & Beloborodov (2014) already found significant curvature and synchrotron photon production around the current sheet of an aligned rotator.…”

Axion dark matter: How to see it?

“…These radio telescope searches were reported to set constraints on the existence of axion dark matter in the micro-electron volt mass ranges (37)(38)(39). Recently, major theoretical uncertainties have also been addressed on the basis of advanced simulation and modeling to estimate the expected signal in a more reliable fashion (40)(41)(42).…”