Pulsar electrodynamics: Relativistic kinetic theory of radiative plasmas—collective phenomena and their radiation

Abstract

The classical modelling of radiation by accelerated charged particles in pulsars predicts a cutoff in photon energy at around 25GeV. Whilst this is broadly consistent with observations, the classical treatment is not self-consistent, and cannot be extended to explain the rare high-energy detections of photons in the 100s of GeV range. In this paper we revisit the theoretical modelling of high-energy radiation processes in very strong electromagnetic fields, in the context of both single particles and collective plasmas. There are no classical constraints on this description. We find that there is indeed a critical energy of around 50 GeV that arises naturally in this self-consistent treatment, but rather than being a cutoff , this critical energy signals a transition from radiation that is classical to a quasi-quantum description, in which the particle is able to radiate almost its total energy in a single event. This new modelling therefore places pulsar radiation processes on a more secure physical basis, and admits the possibility of the production of TeV photons in a self-consistent way.

Ultra-relativistic electrostatic Bernstein waves

“…We consider the relevant value of S 2 p here to approach zero if we wish to apply our theory of ultra-relativistic Bernstein waves to pulsar atmospheres. Bernstein modes, being travelling electrostatic disturbances, are attractive in the pulsar context since they offer the possibility of avoiding the intrinsic density instability that afflicts cold pair-plasma oscillations [20]; such static oscillations are known to generate a coherent electromagnetic response [21] that is implicated in pulsar emission mechanisms, and the electrodynamics of the pulsar atmosphere makes electrostatic disturbances inevitable [12]. However, electrostatic oscillations in the cold plasma limit are confined spatially, and do not travel beyond their initiation site; consequently finite amplitude disturbances deplete the ambient plasma density, leading to unphysical instabilities.…”

“…We are interested in astrophysical electron-positron plasmas, which are expected to be highly relativistic, and thus requiring a 1. The dynamics of highly relativistic electronpositron plasmas in pulsar atmospheres has been a topic of discussion in the recent literature, from compressive shock acceleration [10], to streaming flows [11,12], electromagnetic waves [13,14] and electrostatic modes [15]. In each case, the relativistic Maxwell-Boltzmann-Jüttner distribution function [16] plays a key role in characterizing the behaviour, with the central parameter a taking very small values.…”