A New Approach to Searching for Dark Matter Signals in Fermi-LAT Gamma Rays

Abstract

Several cosmic ray experiments have measured excesses in electrons and positrons, relative to standard backgrounds, for energies from ~ 10 GeV - 1 TeV. These excesses could be due to new astrophysical sources, but an explanation in which the electrons and positrons are dark matter annihilation or decay products is also consistent. Fortunately, the Fermi-LAT diffuse gamma ray measurements can further test these models, since the electrons and positrons produce gamma rays in their interactions in the interstellar medium. Although the dark matter gamma ray signal consistent with the local electron and positron measurements should be quite large, as we review, there are substantial uncertainties in the modeling of diffuse backgrounds and, additionally, experimental uncertainties that make it difficult to claim a dark matter discovery. In this paper, we introduce an alternative method for understanding the diffuse gamma ray spectrum in which we take the intensity ratio in each energy bin of two different regions of the sky, thereby canceling common systematic uncertainties. For many spectra, this ratio fits well to a power law with a single break in energy. The two measured exponent indices are a robust discriminant between candidate models, and we demonstrate that dark matter annihilation scenarios can predict index values that require "extreme" parameters for background-only explanations.

v1: 11 pages, 7 figures, 1 table, revtex4; v2: 13 pages, 8 figures, 1 table, revtex4, Figure 4 added, minor additions made to text, references added, conclusions unchanged, published version

References in corpus (37)

• Observation of an anomalous positron abundance in the cosmic radiation
• A Theory of Dark Matter
• Measurement of the Cosmic Ray e+ plus e- spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
• Cosmology and Astrophysics of Minimal Dark Matter
• A new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiation
• Probing the ATIC peak in the cosmic-ray electron spectrum with H.E.S.S
• Cosmic-ray positron fraction measurement from 1 to 30 GeV with AMS-01
• The origin of the positron excess in cosmic rays
• A blueprint for detecting supersymmetric dark matter in the Galactic halo
• On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope
• Gamma-ray and radio tests of the e+e- excess from DM annihilations
• Dark Matter Interpretations of the Electron/Positron Excesses after FERMI
• Pulsars versus Dark Matter Interpretation of ATIC/PAMELA
• Constraints on Cosmological Dark Matter Annihilation from the Fermi-LAT Isotropic Diffuse Gamma-Ray Measurement
• Implications of High-Resolution Simulations on Indirect Dark Matter Searches
• High-energy antiprotons from old supernova remnants
• Pre-launch estimates for GLAST sensitivity to Dark Matter annihilation signals
• Inverse Compton constraints on the Dark Matter e+e- excesses
• Indirect Dark Matter Detection from Dwarf Satellites: Joint Expectations from Astrophysics and Supersymmetry
• Gamma rays and positrons from a decaying hidden gauge boson
• Dark Matter Signals from Cascade Annihilations
• Cosmic Signals from the Hidden Sector
• A Cosmic Ray Positron Anisotropy due to Two Middle-Aged, Nearby Pulsars?
• Discriminating different scenarios to account for the cosmic $e^{\pm }$ excess by synchrotron and inverse Compton radiation
• Conservative Constraints on Dark Matter Annihilation into Gamma Rays
• Dark matter and sub-GeV hidden U(1) in GMSB models
• Dark matter and pulsar signals for Fermi LAT, PAMELA, ATIC, HESS and WMAP data
• TeV Scale Singlet Dark Matter
• Decaying Hidden Gauge Boson and the PAMELA and ATIC/PPB-BETS Anomalies
• Extracting the Gamma Ray Signal from Dark Matter Annihilation in the Galactic Center Region
• The Contribution Of Inverse Compton Scattering To The Diffuse Extragalactic Gamma-Ray Background From Annihilating Dark Matter
• Optimal angular window for observing Dark Matter annihilation from the Galactic Center region: the case of gamma-ray lines
• The Dark Matter Annihilation Signal from Dwarf Galaxies and Subhalos
• Testing the Dark Matter Interpretation of the PAMELA Excess through Measurements of the Galactic Diffuse Emission
• Astrophysical Uncertainties in the Cosmic Ray Electron and Positron Spectrum From Annihilating Dark Matter
• The Fermi gamma-ray spectrum of the inner galaxy: Implications for annihilating dark matter
• Inhomogeneity in the Supernova Remnants as a Natural Explanation of the PAMELA/ATIC Observations