Implications of a Possible Spectral Structure of Cosmic-ray Protons Unveiled by the DAMPE

Lin Nie, Yang Liu, Zejun Jiang

Published 2023-06-07Version 1

The recent observations revealed that the cosmic-ray (CR) proton spectrum showed a complex structure: the hardening at $\rm \sim 200\,GeV$ and softening at $\rm \sim 10\,TeV$. However, so far the physical origins of this spectral feature remain strongly debated. In this work, we simulate the acceleration of cosmic-ray protons in a nearby Supernova remnant (SNR) by solving numerically the hydrodynamic equations and the equation for the quasi-isotropic CR momentum distribution in the spherically symmetrical case to derive the spectrum of protons injected into the interstellar medium (ISM), and then simulate the propagation process of those accelerated CR particles to calculate the proton fluxes reaching the Earth. Besides, we use the DRAGON numerical code to calculate the large-scale cosmic-ray proton spectrum. Our simulated results are in good agreement with the observed data (including the observed data of proton fluxes and dipole anisotropy). We conclude that the spectral feature of cosmic-ray protons in this energy band may originate from the superposition of the distribution from the nearby SNR and background diffusive cosmic-ray component. We find that the release of particles from this nearby SNR has a time delay. Besides, it can be found that the nonlinear response of energetic particles, release time of CR protons, and age of the local SNR can leave strong signatures in the spectrum of the resulting CR proton fluxes.