Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope (0910.2998v2)

Abstract: We study the gamma rays observed by the Fermi Gamma Ray Space Telescope from the direction of the Galactic Center and find that their angular distribution and energy spectrum are well described by a dark matter annihilation scenario. In particular, we find a good fit to the data for dark matter particles with a 25-30 GeV mass, an annihilation cross section of ~9x10^-26 cm^3/s, and that are distributed with a cusped halo profile within the inner kiloparsec of the Galaxy. We cannot, however, exclude the possibility that these photons originate from an astrophysical source or sources with a similar morphology and spectral shape to those predicted in an annihilating dark matter scenario.

• The paper identifies gamma ray patterns from the Galactic Center that match predictions for dark matter annihilation of a 25-30 GeV particle.
• It demonstrates an annihilation cross-section near 9×10⁻²⁶ cm³/s and a steeper, cusped halo density profile compared to standard models.
• The research highlights the need for cross-validating with other astrophysical sources to conclusively distinguish dark matter signals from alternative gamma ray emissions.

Analysis of Potential Dark Matter Annihilation Observational Data in the Inner Milky Way

The paper conducted by Goodenough and Hooper presents an exploration aimed at identifying potential evidence of dark matter annihilation using data acquired from the Fermi Gamma Ray Space Telescope (FGST). By analyzing gamma rays from the Galactic Center, the authors sought to ascertain patterns consistent with theoretical predictions of dark matter annihilation events.

Key Findings

1. Gamma Ray Distribution and Energy Spectrum:
   • The gamma ray data observed suggests an angular distribution and energy profile consistent with dark matter particles annihilating at a mass of approximately 25-30 GeV.
   • They propose an annihilation cross-section of roughly $9 \times 10^{-26} \, \text{cm}^3/\text{s}$, which is marginally higher than traditional estimates for thermal relics.
2. Halo Density Profile:
   • The data supports a cusped halo distribution, slightly steeper than the Navarro-Frenk-White (NFW) halo profile—specifically, a configuration where $\rho(r) \propto r^{-1.1}$.
   • This observation aligns with expectations of increased dark matter density in the Galactic Center, explaining the intensity of gamma radiation detected.
3. Interpretation Challenges:
   • Despite compelling data, astrophysical scenarios cannot be disregarded completely, as similar gamma ray features could originate from sources in the Galactic Center, such as the black hole (Sgr A*), supernova remnants, or various massive star clusters.
   • The analytical model involves fitting multiple gamma ray sources, including pulsars or supernova remnants, which could confound results attributed solely to dark matter annihilation.
4. Spectrum Analysis:
   • The gamma ray spectrum exhibited a distinctive peak around 1-5 GeV, consistent with expectations from dark matter annihilation producing gamma rays through hadronic final states (e.g., $b\bar{b}$).
   • The results suggest the possibility of using gamma ray data to differentiate between diffuse backgrounds and annihilation signals, albeit with cautious interpretation due to potential astrophysical interference.

Implications and Future Directions

Given the model postulates a dark matter particle mass and profile compatible with the emission data, further investigation through cross-validation with different tools and methodologies is warranted. This includes:

• Comparative Analysis: Data from other gamma-ray observational facilities like the HESS, MAGIC, and VERITAS could be juxtaposed to examine coherent gamma photon signatures contributing to the narrative of dark matter annihilation.
• Complementary Detection Avenues: Pursue indirect detection strategies through synchrotron or inverse Compton scattering rays potentially associated with dark matter decay products.
• Refinement of Halo Modelling: The hypothesis of a steeper halo density profile warrants further simulation, potentially incorporating emergent theories on baryonic interactions and condensation at the core Galactic Center.
• Astrophysical Source Catalogue Enhancement: Develop comprehensive local source catalogs to refine background estimates in gamma ray studies.

Conclusion

This research delineates a robust investigation within a complex astrophysical setting, offering meaningful quantitative benchmarks crucial for ongoing dark matter studies. As the FGST data acquisition progresses, ensuing studies should prioritize refinement of predictive modeling, expansive cross-observatory analysis, and incorporation of alternative astrophysics frameworks to ensure comprehensive understanding and verification of emergent dark matter signatures.