Contribution of the Cygnus bubble to the Galactic cosmic ray spectrum and diffuse $\gamma$-ray emissions

TL;DR

This study models the Cygnus bubble's contribution to cosmic rays and gamma-ray emissions, finding it minimally affects Earth’s CR spectrum but dominates local gamma-ray emissions, highlighting the role of local CR halos.

Contribution

The paper introduces a 3D propagation model incorporating the Cygnus bubble to evaluate its impact on cosmic rays and gamma-ray emissions, providing new insights into local CR sources.

Findings

Cygnus bubble minimally contributes to Earth’s CR spectrum.

CR particles from the bubble dominate local gamma-ray emissions.

Structural fluctuations in gamma-ray emissions are due to the local CR halo.

Abstract

Since the discovery of cosmic rays (CRs) over a century ago, their origin has remained a mystery and a key research question. Recently, the LHAASO experiment identified the first CR super-acceleration source, the Cygnus bubble, which can accelerate CRs to energies exceeding 10 PeV. A pertinent question is: how much does the Cygnus bubble contribute to the CR spectrum observed on Earth? With the aim of answering that question, a 3D propagation analysis was conducted on CRs in this study. The Cygnus bubble was incorporated into our propagation model in order to determine its contributions to the observed spectra. First, we calculated the spectrum and spatial morphology of the Cygnus bubble to reproduce the observed LHAASO data. Subsequently, we calculated the diffuse $\gamma$-ray emissions produced by the CRs from the Cygnus bubble and the energy spectrum of the cosmic ray particles near Earth after propagation. Finally, we utilized a CR spatial-dependent propagation model to calculate the large-scale CR energy spectrum and the resulting diffuse $\gamma$-ray emissions. Our results indicate that: (1) the Cygnus bubble contributes minimally to the CR spectrum observed on Earth, (2) the emissions produced by the CR particles from the Cygnus bubble dominates the diffuse $\gamma$-ray emissions in that region, (3) the structural fluctuations of the diffuse $\gamma$-ray emissions observed by LHAASO are likely due to the local CR halo. We anticipate that LHAASO will identify more CR halo sources to validate our model.