Multi-band Emission up to PeV Energy from the Crab Nebula in a Spatially Dependent Lepto-hadronic Model

TL;DR

This paper models multi-band emission from the Crab Nebula using a spatially dependent lepto-hadronic approach, successfully reproducing observed spectra and predicting neutrino fluxes, with implications for understanding particle acceleration.

Contribution

It introduces a spatially dependent lepto-hadronic model that simulates the Crab Nebula's evolution and reproduces multi-band spectra, including high-energy gamma-rays and neutrino flux predictions.

Findings

Observed spectra are well reproduced with reasonable parameters.

High-energy photons (>200 TeV) mainly originate from hadronic interactions.

Predicted neutrino fluxes are below current detection sensitivities.

Abstract

Multi-band emission from radio to ultra-high energy gamma-rays in the Crab Nebula has been detected. To explain the observed results, non-thermal photon production \textbf{in} the Crab Nebula is carefully studied in a spatially dependent lepto-hadronic model. In our model, the dynamical evolution of the PWN is simulated in a spherically symmetric system. Both electrons and protons are accelerated at the termination shock. The relevant particle propagation equations as well as the photon evolving equation are simultaneously solved. For the Crab Nebula, our results reveal that the observed multi-band photon spectra can be well reproduced with reasonable model parameters. In particular, the photons with energy $\gtrsim 200$ TeV are mainly contributed by the hadronic component via proton-proton interaction. The contribution of the hadronic component depends on both proton spectral index $\alpha_{\rm p}$ and number density $n_{\rm H}$ of medium within the PWN. Besides, high energy neutrino fluxes are predicted with variable proton spectral indices. The predicted fluxes are not only far below the sensitivities of current neutrino observatories, but also beneath the atmospheric neutrino background with energy less than $\sim 40$ TeV. Moreover, the calculated radial profiles of surface brightness and spectral index are presented.