Hadronic Re-Acceleration at the Crab Pulsar Wind Termination Shock as a Source of PeV Gamma-Rays

TL;DR

This paper explores a novel hadronic re-acceleration mechanism at the Crab pulsar wind termination shock as a potential source of PeV gamma-rays, supported by particle transport simulations.

Contribution

It introduces a new scenario where hadrons diffuse into the nebula and are re-accelerated at the termination shock, explaining the highest energy gamma-ray emission.

Findings

Re-acceleration of hadrons is feasible over the Crab's lifetime.

The proposed mechanism can account for PeV gamma-ray production.

Particle transport simulations support the viability of the scenario.

Abstract

Recent results from LHAASO and Tibet AS$\gamma$ suggest that the Crab Nebula's gamma-ray spectrum extends to the PeV energy range, however the production mechanisms of this highest energy emission remain unclear. It has been postulated that a secondary component of hadronic emission could explain the highest energy gamma-ray flux points, however the origin and acceleration mechanism for this hadronic population has yet to be explained. We postulate one scenario in which hadrons diffuse over time into the Crab pulsar wind nebula from the surrounding supernova ejecta, and are subsequently re-accelerated by the pulsar wind termination shock. We present results of direct particle transport simulations (including radial evolution) to determine if this scenario is viable over the lifetime of the Crab system.