Galactic Center Radio Constraints on Gamma-Ray Lines from Dark Matter Annihilation

Abstract: Recent evidence for one or more gamma-ray lines at ~ 130 GeV in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to Z{\gamma} or H{\gamma} with an annihilation cross section, <\sigma v> ~ 10^{-27} cm^3 s^{-1}. We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from the decay of the Z or the H boson only in the Galactic Center against radio data from the same region in the Galactic Center. We find that the radio data from single dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes such as LWA, VLA-Low and LOFAR, and future radio telescopes like SKA, which are sensitive to annihilation cross sections as small as 10^{-28} cm^3 s^{-1}, can confirm or rule out this scenario very soon. We discuss the assumptions on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to Z{\gamma} or H{\gamma}.

• The paper demonstrates that synchrotron emission from dark matter annihilation in the Galactic Center can independently constrain the hypothesis behind the 130 GeV gamma-ray line.
• It employs radio data at 330 MHz and 408 MHz along with varied dark matter profiles to integrate synchrotron flux and compare it with observational measurements.
• The analysis indicates that existing and upcoming radio telescopes could probe annihilation cross-sections down to 10⁻²⁸ cm³ s⁻¹, complementing gamma-ray studies.

Overview of Galactic Center Radio Constraints on Gamma-Ray Lines from Dark Matter Annihilation

This paper investigates the hypothesis that gamma-ray lines observed at approximately 130 GeV in Fermi-LAT data from the Galactic Center (GC) could originate from dark matter (DM) annihilation to $Z\gamma$ or $H\gamma$. The authors assess the potential constraints posed by radio data from the GC, focusing on synchrotron radiation produced by decay products of $Z$ or $H$ bosons emitted in DM annihilations.

Methodology and Analysis

The paper employs a multi-faceted approach to examine the implications of DM annihilation for radio emissions in the GC. It utilizes radio data from single-dish telescopes at 330 MHz and 408 MHz to establish constraints on DM self-annihilation cross-sections, assuming a contracted Navarro-Frenk-White (NFW) DM density profile. The analysis relies on integrating synchrotron flux calculations over specified regions of interest around the GC and comparing these to observational data.

The authors systematically address variations in their results by exploring different DM profiles, such as the Einasto profile and an exponentially contracted NFW profile, and by considering different configurations and magnitudes of galactic magnetic fields. The synchrotron radiation is computed using loss rates associated with inverse Compton scattering, bremsstrahlung, and synchrotron processes, acknowledging the necessity to account for magnetic fields and background radiation density profiles in the GC.

Results and Conclusions

The results suggest that existing radio data only marginally constrain the DM annihilation hypothesis under the considered scenarios. However, the analysis indicates that already-operational and near-future radio telescopes, such as LWA, VLA-Low, LOFAR, and the upcoming SKA, possess the sensitivity to provide significant constraints. These facilities could potentially validate or refute the DM interpretation of gamma-ray lines by probing annihilation cross-sections down to approximately $10^{-28} \, \rm{cm^3\,s^{-1}}$.

The paper's conclusions stress the importance of independent validation of the DM nature of the gamma-ray lines, emphasizing how this investigation complements gamma-ray studies by allowing the exploration of synchrotron signatures in the radio spectrum. It highlights potential future developments in instrumentation and the necessity for high-sensitivity radio observations centered on the GC.

Implications and Future Directions

The work emphasizes the role of radio observations in the indirect detection of DM and the broader significance of multi-wavelength approaches in understanding DM annihilation processes. The results implicate that the proposed method can serve as a robust, model-independent test of dark matter properties, particularly in constraining viable DM models without reliance on specific DM particle physics assumptions.

The study paves the way for further investigations into the radio signature of DM interactions, suggesting collaborations with radio astronomy groups to employ low-frequency observations. Such advances are crucial for providing complementary constraints to those obtained from gamma-ray and other high-energy astrophysical observations.

Given the potential implications for DM research, this work anticipates future enhancements in radio telescope capabilities which can significantly refine our understanding of DM and its potential interactions, advancing the search for its elusive particle identity.