Hadronic emission from the environment of the Crab Pulsar Wind Nebula by re-accelerated particles

Context. The observation of peta-electronvolt (PeV) γ -ray photons from the Crab Nebula by the Large High Altitude Air Shower Observatory (LHAASO) has revitalised the possibility of a secondary population of hadrons producing the highest energy emission through neutral pion decay. Despite previous studies modelling this population, the origin of such high-energy hadronic particles remains unclear. Aims. We consider possible acceleration scenarios for multi-PeV particles in the Crab Nebula environment, including one in which high-energy protons produced at the supernova remnant’s outer shock diffuse into the pulsar wind nebula (PWN). Particles that reach the Crab Pulsar’s wind termination shock can be accelerated to the required energies, and subsequently interact with the dense filaments surrounding the nebula. Methods. We performed particle transport simulations of this scenario, including the effects of the expansion of the PWN into the surrounding supernova ejecta. Results. We find that this results in PeV photons being produced over the lifetime of the Crab system, without over-estimating the flux at lower energies or exceeding the energy budget of the Crab Pulsar. This results in a reasonable match with the LHAASO data at the highest energies. We also present predictions for the resulting all-flavour neutrino flux, finding it to be approximately an order of magnitude below the sensitivity of current generation instruments.