Astrophysical and Dark Matter Interpretations of Extended Gamma-Ray Emission from the Galactic Center (1402.4090v3)

Abstract: We construct empirical models of the diffuse gamma-ray background toward the Galactic Center. Including all known point sources and a template of emission associated with interactions of cosmic rays with molecular gas, we show that the extended emission observed previously in the Fermi Large Area Telescope data toward the Galactic Center is detected at high significance for all permutations of the diffuse model components. However, we find that the fluxes and spectra of the sources in our model change significantly depending on the background model. In particular, the spectrum of the central Sgr A$^\ast$ source is less steep than in previous works and the recovered spectrum of the extended emission has large systematic uncertainties, especially at lower energies. If the extended emission is interpreted to be due to dark matter annihilation, we find annihilation into pure $b$-quark and $\tau$-lepton channels to be statistically equivalent goodness of fits. In the case of the pure $b$-quark channel, we find a dark matter mass of $39.4\left(^{+3.7}_{-2.9}\rm\ stat.\right)\left(\pm 7.9\rm\ sys.\right)\rm\ GeV$, while a pure $\tau^{+} \tau^{-}$-channel case has an estimated dark matter mass of $9.43\left(^{+0.63}_{-0.52}\rm\ stat.\right)(\pm 1.2\rm\ sys.)\ GeV$. Alternatively, if the extended emission is interpreted to be astrophysical in origin such as due to unresolved millisecond pulsars, we obtain strong bounds on dark matter annihilation, although systematic uncertainties due to the dependence on the background models are significant.

• The paper constructs comprehensive empirical models that integrate point sources and cosmic-ray interactions to account for the gamma-ray flux at the GC.
• The paper evaluates dark matter interpretations by assessing multiple annihilation channels, yielding best-fit DM masses of approximately 39.4 GeV and 9.43 GeV.
• The paper sets stringent constraints on astrophysical sources by emphasizing the importance of diffuse background modeling in distinguishing DM signals from unresolved millisecond pulsars.

Evaluation of Gamma-Ray Emission Models from the Galactic Center

The paper authored by Abazajian et al. engages in an in-depth analysis of the extended gamma-ray emission detected towards the Galactic Center (GC), leveraging data from the Fermi Large Area Telescope (LAT). This paper pursues two main avenues of interpretation: the emission being attributable to dark matter (DM) annihilation or of purely astrophysical origin. The authors introduce boosted models incorporating comprehensive empirical data to shed light on the diffuse gamma-ray background towards the GC. The comprehensive treatment of the background model components demonstrates the importance of accounting for systematic uncertainties in the observed gamma-ray emission spectra.

Summary of Key Findings

1. Astrophysical Modeling and Detection: The paper constructs empirical models that incorporate all relevant point sources, as well as templates associated with interactions of cosmic rays with molecular gas. Such models uncover the significance of background model permutations on the flux and spectra of observed sources. They show an alternate perspective on previous findings regarding Sagittarius A* (Sgr A*) by indicating a less steep spectrum, and highlight systematic uncertainties in the recovered spectra of extended emissions, particularly at low energies.
2. Dark Matter Annihilation Interpretation: Interpreting the extended gamma-ray emission as due to DM annihilation, the paper evaluates different annihilation channels. Using a variety of background model permutations, they find that DM annihilation into $b$-quark and $\tau$-lepton channels yields statistically equivalent fits, estimating DM particle masses at approximately 39.4 GeV for the $b$-quark, and 9.43 GeV for the $\tau^{+} \tau^{-}$ channels. However, these findings are heavily influenced by assumptions regarding diffusion models.
3. Systematic Uncertainties and Astrophysical Origins: When shifting the interpretation towards an astrophysical origin, such as unresolved millisecond pulsars (MSPs), this paper sets stringent bounds on potential DM annihilation. These bounds correlate astro-physical phenomena with astrophysical sources, given the high uncertainties resulting from dependencies on diffuse background models, showcasing the robust statistical detection of astrophysical emission from the GC region.

Implications and Future Considerations

The paper highlights critical implications for both theoretical and observational approaches to understanding the GC's high-energy environment. The strong statistical detection of extended emission compatible with annihilating DM underscores the importance of continued exploration of dark matter candidates and their potential interactions. Moreover, the possibility of the emission being primarily astrophysical, notably from MSPs, insinuates the need for detailed radio and gamma-ray surveys to refine the emission source characterization.

Future investigations need to address the intricacies involved in modeling the diffuse backgrounds more explicitly, considering both low-energy thresholds and line-broadening effects in the gamma-ray spectra. The nuanced understanding of the diffuse emission spectra's dependency on model assumptions demands a reinfor-ced focus on rigorous statistical frameworks and cross-wavelength analysis to eliminate astrophysical ambiguities around the GC environments.

In conclusion, this research paper successfully advances our understanding of high-energy emissions at the GC by introducing a balanced approach that encapsulates both DM and astrophysical entities in a cohesive framework. This method facilitates a nuanced analysis suited for addressing the complexities involved in interpreting cosmic phenomena. The paper underscores the critical need for a multi-perspective lens when analyzing cosmic gamma-ray data, inviting continued dialogue and collaboration within the astrophysical and particle physics communities.