Search for a Dark Matter Annihilation Signal from the Galactic Center Halo with H.E.S.S.

A. Abramowski et al. (H.E.S.S. Collaboration)

Phys. Rev. Lett. 106, 161301 – Published 18 April 2011

Abstract

A search for a very-high-energy (VHE; $\geq 100 GeV$ ) $γ$ -ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance $r \sim 45 - 150 pc$ from the Galactic center. The background-subtracted $γ$ -ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) $γ$ -ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual $γ$ -ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section $⟨ σ v ⟩$ as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of $\sim 1 TeV$ , values for $⟨ σ v ⟩$ above $3 \times 10^{- 25} {cm}^{3} s^{- 1}$ are excluded for the Einasto density profile.

Received 4 November 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.161301

Authors & Affiliations

Click to Expand

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 106, Iss. 16 — 22 April 2011

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Comparison of the Galactic DM halo profiles used in this analysis. The parameters for the NFW and Einasto profiles are taken from [25]. An isothermal profile [24], exhibiting a flat DM density out to a galactocentric distance of 1 kpc, is shown for comparison. All profiles are normalized to the local DM density ( $ρ_{0} = 0.39 GeV / {cm}^{3}$ [29] at a distance of 8.5 kpc from the GC). The source region and the region used for background estimation are indicated. Note that the predicted DM density is always larger in the source region, except for the isothermal profile, which is included for completeness.
Reuse & Permissions
Figure 2
Illustration of the cosmic-ray background subtraction technique for a telescope pointing position below the Galactic plane (depicted by the star). Note that this is only one of the several different pointing positions of the data set. The DM source region is the green area inside the black contours, centered on the GC (black triangle). Yellow regions are excluded from the analysis because of contamination by astrophysical sources. Corresponding areas for background estimation (red regions) are constructed by rotating individual pixels of size $0.02 ° \times 0.02 °$ of the source region around the pointing position by 90°, 180°, and 270°. This choice guarantees similar $γ$ -ray detection efficiency in both the source and background regions. As an example, pixels labeled 1 and 2 serve as background control regions for pixel 0. Pixel 3 is not considered for background estimation because it is located in an excluded region. Pixels in the source region, for which no background pixels can be constructed, are not considered in the analysis for this particular pointing position and are left blank.
Reuse & Permissions
Figure 3
Top panel: Reconstructed differential flux $F_{Src / Bg}$ , weighted with $E^{2.7}$ for better visibility, obtained for the source and background regions as defined in the text. The units are ${TeV}^{1.7} m^{- 2} s^{- 1} {sr}^{- 1}$ . Because of an energy-dependent selection efficiency and the use of effective areas obtained from $γ$ -ray simulations, the reconstructed spectra are modified compared to the cosmic-ray power-law spectrum measured on Earth. Bottom panel: Flux residua $F_{res} / Δ F_{res}$ , where $F_{res} = F_{Src} - F_{Bg}$ and $Δ F_{res}$ is the statistical error on $F_{res}$ . The residual flux is compatible with a null measurement. Comparable null residuals are obtained when varying the radius of the source region, subdividing the data set into different time periods or observation positions, or analyzing each half of the source region separately.
Reuse & Permissions
Figure 4
Upper limits (at 95% CL) on the velocity-weighted annihilation cross section $⟨ σ v ⟩$ as a function of the DM particle mass $m_{χ}$ for the Einasto and NFW density profiles. The best sensitivity is achieved at $m_{χ} \sim 1 TeV$ . For comparison, the best limits derived from observations of dwarf galaxies at very high energies, i.e., Sgr Dwarf [10], Willman 1, Ursa Minor [15], and Draco [9], using in all cases NFW shaped DM profiles, are shown. Similar to the sky region investigated in the presented analysis, dwarf galaxies are objects free of astrophysical background sources. The green points represent DarkSUSY models [32], which are in agreement with WMAP and collider constraints and were obtained with a random scan of the mSUGRA parameter space using the following parameter ranges: $10 GeV < M_{0} < 1000 GeV$ , $10 GeV < M_{1 / 2} < 1000 GeV$ , $A_{0} = 0$ , $0 < \tan β < 60$ , $sgn (μ) = \pm 1$ .
Reuse & Permissions

Physical Review Letters