Diffuse Cosmic Rays Shining in the Galactic Center: A Novel Interpretation of H.E.S.S. and Fermi-LAT γ-Ray Data

Area of Science:

• Astrophysics
• High-energy astrophysics
• Gamma-ray astronomy

Background:

• The Galactic Center (GC) and Galactic Ridge (GR) exhibit complex gamma-ray emissions.
• Understanding the origin of these emissions is crucial for astrophysics and particle physics.

Purpose of the Study:

• To provide a novel interpretation of gamma-ray diffuse emission in the GC and GR regions.
• To investigate the radial distribution and transport of cosmic rays (CRs) in the Milky Way.

Main Methods:

• Data-driven analysis of Fermi-LAT PASS8 data, extending H.E.S.S. spectra down to a few GeV.
• Utilizing a cosmic-ray transport model with a position-dependent diffusion coefficient.

Main Results:

• Inferred primary cosmic-ray radial distribution between 0.1 and 3 TeV.
• The position-dependent diffusion coefficient model reproduces observed CR spectral index variations.
• The bulk of GR emission is explained by the interaction of the diffuse Galactic CR sea with gas in the central molecular zone.

Conclusions:

• A large-scale diffuse component is significant, naturally explaining most GR emission.
• While a residual central source is detected, its relevance is diminished by the diffuse emission.
• The study does not provide solid evidence for Galactic Center pevatrons, emphasizing the role of the diffuse CR sea.