Diffuse Galactic gamma rays from shock-accelerated cosmic rays

Area of Science:

• Astrophysics
• Particle Physics
• Cosmic Ray Physics

Background:

• Cosmic rays are high-energy particles originating from outer space.
• Understanding their origin and propagation is crucial for astrophysics.
• Previous studies suggested a spectral break in cosmic-ray proton flux.

Purpose of the Study:

• To investigate the spectral shape of shock-accelerated cosmic-ray protons.
• To re-evaluate the claim of a spectral break in cosmic-ray proton flux.
• To explain gamma-ray emission from molecular clouds.

Main Methods:

• Theoretical modeling of particle acceleration at nonrelativistic shocks.
• Analysis of rigidity-dependent escape into the Galactic halo.
• Fitting Fermi Large Area Telescope gamma-ray emission spectra.

Main Results:

• A particle flux proportional to p(-s) (momentum to the power of -s) with s≈2.8 adequately fits the data.
• The previously claimed spectral break is an artifact of using a power law in kinetic energy.
• Uncertainties in nuclear production models were considered.

Conclusions:

• The cosmic-ray proton flux follows a power law in momentum, not kinetic energy.
• The proposed spectral break is not physically supported by the data.
• Shock acceleration and halo escape provide a consistent model for cosmic rays.