Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope (1010.2752v3)

Abstract: We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10 degrees around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25 degrees and 10 degrees from the Galactic Center is well described by a the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25 degrees (~175 parsecs) of the Galactic Center, in contrast, departs from the expectations for by these processes. Instead, we find an additional component of gamma ray emission that is highly concentrated around the Galactic Center. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution (density proportional to r^{-gamma}, with gamma=1.18 to 1.33). The observed spectrum of this component, which peaks at energies between 1-4 GeV (in E^2 units), can be well fit by a 7-10 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of 4.6 x 10^-27 to 5.3 x 10^-26 cm^3/s, depending on how the dark matter distribution is normalized. We also discuss other sources for this emission, including the possibility that much of it originates from the Milky Way's supermassive black hole.

• The paper identifies a concentrated gamma-ray excess within 1.25° of the Galactic Center, consistent with dark matter annihilation profiles.
• It employs detailed emission modeling to separate known astrophysical sources from potential dark matter signals, highlighting a 1-4 GeV spectral peak.
• The study outlines future observational strategies to further validate the dark matter hypothesis and refine theoretical models.

Analysis of Dark Matter Annihilation in the Galactic Center Using Fermi Gamma Ray Space Telescope Data

The research paper titled "Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope," authored by Dan Hooper and Lisa Goodenough, presents a comprehensive analysis of gamma-ray data collected by the Fermi Gamma Ray Space Telescope (FGST) over the initial two years of its mission. The primary aim of this investigation is to either constrain or detect signals indicative of annihilating dark matter in the vicinity of the Galactic Center.

Key Findings and Methodology

1. Observed Emission Profiles: The paper delineates the gamma-ray emission within a 10-degree radius surrounding the Galactic Center into primarily known astrophysical sources. Between 1.25 and 10 degrees from the center, the gamma-ray data is well-explained by cosmic ray interactions leading to pion decay, inverse Compton scattering, and emissions from identified point sources.
2. Excess Within 1.25 Degrees: Within a radius of approximately 1.25 degrees from the Galactic Center, the emission deviates from these expected profiles, suggesting an additional component. The morphology of this excess emission is highly concentrated, consistent with the characteristics of annihilating dark matter with a cusped halo profile, characterized by a density distribution proportional to $r^{-\gamma}$ (where $\gamma$ is between 1.18 and 1.33).
3. Dark Matter Interpretation: The spectral peak of the additional component (1-4 GeV) aligns well with predictions for dark matter particles in the mass range of 7-10 GeV that preferentially annihilate into tau leptons, with a cross-section on the order of $4.6 \times 10^{-27}$ cm$^3$/s to $5.3 \times 10^{-26}$ cm$^3$/s, contingent on the normalization of the dark matter distribution.
4. Alternative Explanations: The authors evaluate other potential sources for this emission, such as contributions from the Milky Way’s central supermassive black hole or alternative cosmic phenomena. Nonetheless, these alternative sources face challenges in explaining the observed angular concentration— one that favors a dark matter hypothesis.

Implications and Future Prospects

The results of this paper bear significant implications for both theoretical astrophysics and the prospects for dark matter detection. The suggested mass and annihilation pathways are notably sympathetic with dark matter candidates also implicated by other astrophysical and direct detection signals, such as those observed by CoGeNT and DAMA. This confluence of evidence may guide future theoretical models in refining dark matter particle properties.

From a practical standpoint, continued and more granular observations with FGST and future telescopes may aid in further isolating these signals, potentially confirming or refining the dark matter interpretation. The methodology utilized here, particularly the separation of gamma-ray sources and careful modeling of emission profiles, presents a robust framework for ongoing and future research.

In conclusion, while the paper stops short of definitively declaring the detection of dark matter annihilation, it marks a significant step forward in identifying candidate signatures that warrant further investigation. As data accumulation and analytical techniques advance, the possibility of obtaining a clearer picture of dark matter behavior at the Galactic Center is promising. This research thus forms a crucial part of the ongoing effort to unravel one of astrophysics' most enigmatic phenomena.