H.E.S.S. observations of the Galactic Center region and their possible dark matter interpretation

TL;DR

This study analyzes H.E.S.S. data from 2004 to investigate whether the Galactic Center TeV gamma-ray emission could arise from dark matter (DM) annihilation or astrophysical processes. By modeling and subtracting the diffuse GC ridge and fitting the central source with PSF-convolved templates, the authors measure a power-law spectrum $F(E) \propto E^{-Γ}$ with $Γ=2.25\pm0.04\,(stat)\pm0.10\,(syst)$ over $160$ GeV to $30$ TeV, and place a 1.2′ upper limit on the source size at 95% CL. They find no significant variability and disfavour conventional DM annihilation geometries, deriving 99% CL upper limits on the velocity-weighted cross section $⟨σv⟩$ of order $10^{-24}$–$10^{-23}$ cm$^3$ s$^{-1}$ depending on halo assumptions; adiabatic compression could boost the signal by up to ~10^3, partially mitigating these constraints. The results indicate that the bulk of the GC TeV emission is likely astrophysical, while still providing stringent constraints on DM models in the GC region and illustrating a robust framework for separating DM and astrophysical components in IACT data.

Abstract

The detection of gamma-rays from the source HESS J1745-290 in the Galactic Center (GC) region with the H.E.S.S. array of Cherenkov telescopes in 2004 is presented. After subtraction of the diffuse gamma-ray emission from the GC ridge, the source is compatible with a point-source with spatial extent less than 1.2'(stat.) (95% CL). The measured energy spectrum above 160 GeV is compatible with a power-law with photon index of 2.25 +/- 0.04(stat.) +/- 0.10 (syst.) and no significant flux variation is detected. These measurements are discussed in the framework of dark matter annihilation. It is found that the bulk of the VHE emission must have non-dark-matter origin. Loose constraints on the velocity-weighted annihilation cross section <sigma.v> are derived assuming the presence of an astrophysical non-dark-matter gamma-ray contribution.

Figures (2)

• Figure 1: (Color online) Background-subtracted distribution of the angle $\theta$ between the $\gamma$-ray direction and the position of Sgr A*. Circles: all detected $\gamma$-rays events. Open triangles: central object after subtraction of the $\gamma$-ray diffuse emission model (see text). Line: calculated PSF normalized to the number of $\gamma$-rays within $0.1^{\circ}$ after subtraction is also shown. The distribution of events after subtraction matches the calculated PSF while the initial distribution shows a significant tail. The variation of the PSF related to the source energy spectrum, zenith angle and offset position in the field of view are taken into account. Insert: same distribution for the point-like source PKS 2155-304 PKS2155. The calculated PSF (line) also matches the data.
• Figure 2: (Color online) Spectral energy density $E^2\times \mathrm{d}N/\mathrm{d}E$ of $\gamma$-rays from the GC source, for the 2004 data (full points) and 2003 data hess (open points). Upper limits are 95% CL. The shaded area shows the power-law fit $\mathrm{d}N/\mathrm{d}E \sim E^{-\Gamma}$. The dashed line illustrates typical spectra of phenomenological MSSM DM annihilation for best fit neutralino masses of 14 TeV. The dotted line shows the distribution predicted for KK DM with a mass of 5 TeV. The solid line gives the spectrum of a 10 TeV DM particle annihilating into $\tau^+\tau^-$ (30%) and $b\bar{b}$ (70%).