On a possible origin of the gamma-ray excess around the Galactic Center

Abstract

Recent observations of gamma-rays with the Fermi Large Area Telescope (LAT) in the direction of the inner Galaxy revealed a mysterious GeV excess. Its intensity is significantly above predictions of the standard model of cosmic rays (CRs) generation and propagation with a peak in the spectrum around a few GeV. Popular interpretations of this excess are due to either spherically distributed annihilating dark matter (DM) or abnormal population of millisecond pulsars. We suggested an alternative explanation of the excess through the CR interactions with molecular clouds in the Galactic Center (GC) region. We assumed that the excess could be imitated by the emission of molecular clouds with depleted density of CRs with energies below ~ 10 GeV inside. A novelty of our work is in detailed elaboration of the depletion mechanism of CRs with the mentioned energies through the "barrier" near the cloud edge formed by the self-excited MHD turbulence. Such depletion of CRs inside the clouds may be a reason of deficit of gamma rays from the Central Molecular Zone (CMZ) at energies below few GeV. This in turn changes the ratio between various emission components at those energies, and may potentially absorb the GeV excess by simple renormalization of key components.

arXiv comment7 pages, 1 figure. This is slightly refined version of this paper published in the special issue "Gamma Ray Signals from Dark Matter" of the journal "Symmetry"

References in corpus (21)

• Observation of an anomalous positron abundance in the cosmic radiation
• Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
• Production and propagation of cosmic-ray positrons and electrons
• Detection of a Gamma-Ray Source in the Galactic Center Consistent with Extended Emission from Dark Matter Annihilation and Concentrated Astrophysical Emission
• Background model systematics for the Fermi GeV excess
• Development of the Model of Galactic Interstellar Emission for Standard Point-Source Analysis of Fermi Large Area Telescope Data
• The Fermi Galactic Center GeV Excess and Implications for Dark Matter
• Parametrization of gamma-ray production cross-sections for pp interactions in a broad proton energy range from the kinematic threshold to PeV energies
• Updated Search for Spectral Lines from Galactic Dark Matter Interactions with Pass 8 Data from the Fermi Large Area Telescope
• Spatial distribution of interstellar gas in the innermost 3 kpc of our Galaxy
• Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center
• Interstellar dust charging in dense molecular clouds: cosmic ray effects
• High-Energy Gamma Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities in the Interstellar Medium
• Interstellar magnetic fields in the Galactic center region
• Strong Evidence that the Galactic Bulge is Shining in Gamma Rays
• The Three-Dimensional Spatial Distribution of Interstellar Gas in the Milky Way: Implications for Cosmic Rays and High-Energy Gamma-Ray Emissions
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• Gamma-ray Astrophysics in the MeV Range: the ASTROGAM Concept and Beyond
• Dark matter searches by the planned gamma-ray telescope GAMMA-400
• Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays
• Molecular Clouds as the Origin of the Fermi Gamma-Ray GeV-Excess