The GeV-TeV Galactic gamma-ray diffuse emission I. Uncertainties in the predictions of the hadronic component

Abstract

The Galactic gamma-ray diffuse emission is currently observed in the GeV-TeV energy range with unprecedented accuracy by the Fermi satellite. Understanding this component is crucial as it provides a background to many different signals such as extragalactic sources or annihilating dark matter. It is timely to reinvestigate how it is calculated and to assess the various uncertainties which are likely to affect the accuracy of the predictions. The Galactic gamma-ray diffuse emission is mostly produced above a few GeV by the interactions of cosmic ray primaries impinging on the interstellar material. The theoretical error on that component is derived by exploring various potential sources of uncertainty. Particular attention is paid to cosmic ray propagation. Nuclear cross sections, the proton and helium fluxes at the Earth, the Galactic radial profile of supernova remnants and the hydrogen distribution can also severely affect the signal. The propagation of cosmic ray species throughout the Galaxy is described in the framework of a semi-analytic two-zone diffusion/convection model. This allows to convert the constraints set by the boron-to-carbon data into a theoretical uncertainty on the diffuse emission. New deconvolutions of the HI and CO sky maps are also used to get the hydrogen distribution within the Galaxy. The thickness of the cosmic ray diffusive halo is found to have a significant effect on the Galactic gamma-ray diffuse emission while the interplay between diffusion and convection has little influence on the signal. The uncertainties related to nuclear cross sections and to the primary cosmic ray fluxes at the Earth are significant. The radial distribution of supernova remnants along the Galactic plane turns out to be a key ingredient. As expected, the predictions are extremely sensitive to the spatial distribution of hydrogen within the Milky Way.

22 pages, 21 figures; Matches published version (references added)

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• Indirect Detection Analysis: Wino Dark Matter Case Study
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• Galactic halo size in the light of recent AMS-02 data
• Extracting limits on Dark Matter annihilation from gamma-ray observations towards dwarf spheroidal galaxies
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• Filamentary Diffusion of Cosmic Rays on Small Scales
• Simulating the Galactic Multi-messenger Emissions with HERMES
• Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy
• Indirect dark matter searches as a probe of degenerate particle spectra
• Probing galactic cosmic ray distribution with TeV gamma-ray sky
• The 130 GeV gamma-ray line and generic dark matter model building constraints from continuum gamma rays, radio and antiproton data
• Why is the Milky Way X-factor Constant?
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• Extracting the size of the cosmic electron-positron anomaly
• Indirect dark matter searches: towards a consistent top-bottom approach for studying the gamma-ray signals and associated backgrounds
• AMS-02 fits Dark Matter
• Galactic Gamma Ray Background from Interactions of Cosmic Rays
• A New Census of the Universe's Entropy
• Absorption spectra of electrified hydrogen molecules