Cosmic Ray Protons in the Inner Galaxy and the Galactic Center Gamma-Ray Excess

Abstract

A gamma-ray excess over background has been claimed in the inner regions of the Galaxy, triggering some excitement about the possibility that the gamma rays originate from the annihilation of dark matter particles. We point out that the existence of such an excess depends on how the diffuse gamma-ray background is defined, and on the procedure employed to fit such background to observations. We demonstrate that a gamma-ray emission with spectral and morphological features closely matching the observed excess arises from a population of cosmic ray protons in the inner Galaxy, and provide proof of principle and arguments for the existence of such a population, most likely originating from local supernova remnants. Specifically, the "Galactic center excess" is readily explained by a recent cosmic-ray injection burst, with an age in the 1-10 kilo-year range, while the extended inner Galaxy excess points to mega-year old injection episodes, continuous or impulsive. We conclude that it is premature to argue that there are no standard astrophysical mechanisms that can explain the excess.

19 pages, 6 figures, v2: Accepted to PRD, v3: Errata Changes Only, v4 Added DOI

References in corpus (11)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• Parameterization of Gamma, e^+/- and Neutrino Spectra Produced by p-p Interaction in Astronomical Environment
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Wild at Heart:-The Particle Astrophysics of the Galactic Centre
• Mechanism for spectral break in cosmic ray proton spectrum from Supernova remnant W44
• The Likely Cause of the EGRET GeV Anomaly and its Implications
• Systematic Effects in Extracting a "Gamma-Ray Haze" from Spatial Templates

Cited by in corpus (50)

• Background model systematics for the Fermi GeV excess
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• A Tale of Tails: Dark Matter Interpretations of the Fermi GeV Excess in Light of Background Model Systematics
• Scalar Simplified Models for Dark Matter
• GeV excess in the Milky Way: The Role of Diffuse Galactic gamma ray Emission template
• Dark Nuclei I: Cosmology and Indirect Detection
• A Comprehensive Search for Dark Matter Annihilation in Dwarf Galaxies
• Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?
• Millisecond pulsars and the Galactic Center gamma-ray excess: the importance of luminosity function and secondary emission
• The characteristics of the Galactic center excess measured with 11 years of Fermi-LAT data
• NMSSM Interpretation of the Galactic Center Excess
• Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic center
• Multi-Step Cascade Annihilations of Dark Matter and the Galactic Center Excess
• Multimessenger constraints on the dark matter interpretation of the Fermi-LAT Galactic center excess
• Antiproton constraints on the GeV gamma-ray excess: a comprehensive analysis
• The Return of the Templates: Revisiting the Galactic Center Excess with Multi-Messenger Observations
• Z' Mediated Dark Matter Models for the Galactic Center Gamma-Ray Excess
• Search for Gamma-ray Emission from Dark Matter Annihilation in the Large Magellanic Cloud with the Fermi Large Area Telescope
• Galactic Center Excess in Gamma Rays from Annihilation of Self-Interacting Dark Matter
• Supersymmetric Sub-Electroweak Scale Dark Matter, the Galactic Center Gamma-ray Excess, and Exotic Decays of the 125 GeV Higgs Boson
• VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies
• Distinguishing Dark Matter from Unresolved Point Sources in the Inner Galaxy with Photon Statistics
• Testing the millisecond pulsar scenario of the Galactic center gamma-ray excess with very high energy gamma-rays
• SUSY Implications from WIMP Annihilation into Scalars at the Galactic Centre
• Effect of Black Holes in Local Dwarf Spheroidal Galaxies on Gamma-Ray Constraints on Dark Matter Annihilation
• Discovery of a New Galactic Center Excess Consistent with Upscattered Starlight
• Les Houches Lectures on Indirect Detection of Dark Matter
• Galactic Center gamma-ray excess from two-Higgs-doublet-portal dark matter
• The Semi-Hooperon: Gamma-ray and anti-proton excesses in the Galactic Center
• Search for $\gamma$-ray emission from dark matter particle interactions from Andromeda and Triangulum Galaxies with the Fermi Large Area Telescope
• Simplified Dark Matter Models Confront the Gamma Ray Excess
• Gamma rays from the Galactic Centre region: a review
• Amplified J-factors in the Galactic Center for velocity-dependent darkmatter annihilation in FIRE simulations
• Dim but not entirely dark: Extracting the Galactic Center Excess' source-count distribution with neural nets
• AMS-02 Positron Excess and Indirect Detection of Three-body Decaying Dark Matter
• Identification of point sources in gamma rays using U-shaped convolutional neural networks and a data challenge
• Cosmic-Ray Models of the Ridge-Like Excess of Gamma Rays in the Galactic Center
• Constraints on dark matter annihilation and decay from the large-scale structure of the nearby universe
• Tau Portal Dark Matter models at the LHC
• Robustness of the Galactic Center Excess Morphology Against Masking
• Constraints on dark matter annihilation from the FAST observation of the Coma Berenices dwarf galaxy
• Muonphilic Dark Matter explanation of gamma-ray galactic center excess: a comprehensive analysis
• Probing the pulsar explanation of the Galactic-Center GeV excess using continuous gravitational-wave searches
• Mind the gap: The discrepancy between simulation and reality drives interpretations of the Galactic Center Excess
• Interpreting the galactic center gamma-ray excess in the NMSSM
• Millisecond Pulsar Kicks Cause Difficulties in Explaining the Galactic Center Gamma-Ray Excess
• Galactic Centre as an efficient source of cosmic rays
• Possible counterpart signal of the Fermi bubbles at the cosmic-ray positrons
• Search for dark matter with IACTs and the Cherenkov Telescope Array
• Dark matter properties implied by gamma ray interstellar emission models