Pulsar Radio Emission Mechanism: Radio Nanoshots as a Low-frequency Afterglow of Relativistic Magnetic Reconnection

Abstract

In this Letter we propose that coherent radio emission of Crab, other young energetic pulsars, and millisecond pulsars is produced in the magnetospheric current sheet beyond the light cylinder. We carry out global and local two-dimensional kinetic plasma simulations of reconnection to illustrate the coherent emission mechanism. Reconnection in the current sheet beyond the light cylinder proceeds in the very efficient plasmoid-dominated regime, and current layer gets fragmented into a dynamic chain of plasmoids which undergo successive coalescence. Mergers of sufficiently large plasmoids produce secondary perpendicular current sheets, which are also plasmoid-unstable. Collisions of plasmoids with each other and with the upstream magnetic field eject fast-magnetosonic waves, which propagate upstream across the background field and successfully escape from the plasma as electromagnetic waves that fall in the radio band. This model successfully explains many important features of the observed radio emission from Crab and other pulsars with high magnetic field at the light cylinder: phase coincidence with the high-energy emission, nano-second duration (nanoshots), and extreme instantaneous brightness of individual pulses.

Emission Mechanisms of Fast Radio Bursts

“…Therefore, the reconnection process produces an emission with wavelength of the order of a few dozens of Larmor radii of particles within the sheet. The fms pulses are clearly observed in simulations of the reconnection in the current sheet [46]; it was found that they take away roughly 0.5% of the magnetic energy dissipated during the reconnection process.…”

Magnetosphere of an orbiting neutron star

“…The latest work also shows that in the reconnection region, radio waves may be emitted by coalescence of magnetic islands in the CS that produces magnetic perturbations propagating away [28,31,52]. For this process, the predicted spectral flux density of the radio waves with the frequency ν is…”

The electromagnetic radiation whose decay violates the inverse-square law: detailed mathematical treatment of an experimentally realized example

“…That the magnetospheric current sheet may be responsible for the observed radiation from rapidly rotating neutron stars has already been put forward in the literature but with an emphasis on the microscale structure of the sheet and magnetic reconnection (Uzdensky & Spitkovsky 2014; Philippov et al. 2019, and the references therein). According to the results obtained here, in contrast, it is the accelerated motion at a superluminal speed of the sharply localized macroscopic distribution pattern of this current sheet that underlies its candidacy as a possible source of the radiation received from such objects.…”