The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter (1402.6703v2)

Abstract: Past studies have identified a spatially extended excess of $\sim$1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics and origin. By applying cuts to the \textit{Fermi} event parameter CTBCORE, we suppress the tails of the point spread function and generate high resolution gamma-ray maps, enabling us to more easily separate the various gamma-ray components. Within these maps, we find the GeV excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 36-51 GeV dark matter particle annihilating to $b\bar{b}$ with an annihilation cross section of $\sigma v = (1-3)\times 10^{-26}$ cm$^3$/s (normalized to a local dark matter density of 0.4 GeV/cm$^3$). Furthermore, we confirm that the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within $\sim$$0.05^{\circ}$ of Sgr A$^*$), showing no sign of elongation along the Galactic Plane. The signal is observed to extend to at least $\simeq10^{\circ}$ from the Galactic Center, disfavoring the possibility that this emission originates from millisecond pulsars.

• The paper demonstrates that the observed 1-3 GeV gamma-ray excess is consistent with predictions for a 36-51 GeV dark matter particle annihilating into bottom quarks.
• It employs advanced filtering techniques on Fermi data to enhance gamma-ray map resolution and minimize leakage from the Galactic disk.
• The findings reinforce dark matter models and provide significant implications for future cosmological observations and detection strategies.

Overview of the Gamma-Ray Signal from the Central Milky Way and Its Interpretation as Dark Matter Annihilation

The analysis of the gamma-ray signal emanating from the center of the Milky Way, as presented by Daylan et al., offers a compelling insight into the potential connection between these emissions and annihilating dark matter. This research revisits the anomalous gamma-ray excess initially identified in previous studies and provides a robust enhancement to the comprehension of this astrophysical signal. The authors utilize data obtained from the Fermi Gamma-Ray Space Telescope and apply advanced methodological refinements to strengthen the evidence supporting a dark matter interpretation.

Gamma-Ray Signal Characterization

The research identifies an excess of 1-3 GeV gamma rays originating from the Galactic Center, characterized by its spherical symmetry and spatial extension up to approximately 10 degrees from the center. This emission's spectrum, angular distribution, and normalization exhibit compatibility with theoretical predictions made for annihilating dark matter models. The research suggests that the signal is well-explained by a 36-51 GeV dark matter particle annihilating primarily into bottom quarks (b-bar), with an annihilation cross-section proximate to $$\langle \sigma v \rangle = (1-3) \times 10^{-26} \, \text{cm}^3/\text{s}$$. Notably, this cross-section aligns closely with the threshold predicted for a thermally produced WIMP (Weakly Interacting Massive Particle), thereby offering a coherent scenario within the framework of standard cosmological models of dark matter.

Methodological Enhancements

The paper meticulously refines previous analyses by adopting an improved technique that filters the gamma-ray data based on event characteristics, enhancing the resolution of the derived gamma-ray maps. By implementing cuts on the Fermi event parameter CTBCORE, the authors achieve a convergence of independent results toward a consistent spectral shape. This methodological advancement minimizes leakage from the Galactic disk and clarifies the origin of the gamma-ray excess. The paper further supports the differentiation of this signal from potential astrophysical sources, such as millisecond pulsars or cosmic-ray interactions with gas, which are statistically improbable to account for the observed shape and spatial distribution.

Implications and Future Directions

The consistent association of the gamma-ray excess with dark matter annihilation, as opposed to alternative astrophysical sources, has profound implications for both theoretical astrophysics and high-energy physics. It both reinforces and constrains theoretical models that posit dark matter as WIMPs within a specific mass and cross-section range. The implications extend to future observational strategies where comprehensive surveys of other potential dark matter-rich regions (such as dwarf spheroidal galaxies or galaxy clusters) might corroborate these findings and laudably strengthen dark matter model formulations.

This paper serves as a keystone for future investigations, encouraging further analytical scrutiny and incentivizing novel detection methodologies that could incontrovertibly validate the dark matter hypothesis. As our understanding of cosmic phenomena expands, the identification of dark matter candidates remains pivotal to unlocking the fundamental nature of our universe. Further instrumental developments and enhanced gamma-ray detection capabilities might imminently provide the data necessary to resolve current ambiguities in dark matter research.

In summary, this paper provides a robust analysis and substantiation of the connection between observed gamma-ray emissions from the central Milky Way and theorized dark matter annihilation. It represents a significant advance in the field, augmenting the credibility of theoretical models and encouraging future exploration into the cosmic prevalence and characteristics of dark matter.