Particle acceleration in superluminal strong waves

TL;DR

This paper investigates electron acceleration mechanisms in superluminal strong waves within pulsar wind nebulae, revealing how primary and secondary waves influence energy gain and radiation, with implications for observed radio knots.

Contribution

It provides a detailed numerical analysis of electron acceleration in superluminal strong waves, highlighting the roles of primary and secondary waves and their effects on radiation signatures.

Findings

Electrons gain nearly equal energy under secondary wave dominance.

Phase-locked electrons are continuously accelerated by primary waves.

Radiation from phase-locked electrons differs from synchro-Compton emission.

Abstract

We calculate the electron acceleration in random superluminal strong waves (SLSWs) and radiation from them by using numerical methods in the context of the termination shock of the pulsar wind nebulae. We pursue the electrons by solving the equation of motion in the analytically expressed electromagnetic turbulences. These consist of primary SLSW and isotropically distributed secondary electromagnetic waves. Under the dominance of the secondary waves, all electrons gain nearly equal energy. On the other hand, when the primary wave is dominant, selective acceleration occurs. The phase of the primary wave felt by the electrons moving nearly along the wavevector changes very slowly compared to the oscillation of the wave, which is called "phase locked", and such electrons are continuously accelerated. This acceleration by SLSWs may play a crucial role in the pre-acceleration for the shock acceleration. In general, the radiation from the phase-locked population is different from the synchro-Compton radiation. However, when the amplitude of the secondary waves is not extremely weaker than that of the primary wave, the typical frequency can be estimated from the synchro-Compton theory by using the secondary waves. The primary wave does not contribute to the radiation, because the SLSW accelerates electrons almost linearly. This radiation can be observed as a radio knot at the upstream of the termination shock of the pulsar wind nebulae without counter parts in higher frequency range.