Combined Dark Matter searches towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, HESS, MAGIC and VERITAS (1909.06310v1)

Abstract: The search for Dark Matter (DM) has great potential to reveal physics beyond the Standard Model. As such, searches for evidence of DM particles are being carried out using a wide range of techniques, such as direct searches for DM particles, searches for DM produced with colliders, and indirect searches for the Standard Model annihilation products of DM. Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect Dark Matter searches due to their relatively high DM content and negligible expected astrophysical background. A collaboration was formed to maximise the sensitivity of DM searches towards dSphs by combining for the first time dSph data from three imaging air Cherenkov telescope (IACT) arrays: HESS, MAGIC, and VERITAS; the Fermi-LAT satellite, and the water Cherenkov detector HAWC. Due to the diverse nature of the instruments involved, each experiment will analyse their individual datasets from multiple targets and then the results will be combined at the likelihood level. For consistency of the likelihoods across the five experiments, a common approach is used to treat the astrophysical factor (J-Factor) for each target and an agreed set of annihilation channels are considered. We also agree on a common statistical approach and treatment of instrumental systematic uncertainties. The results are presented in terms of constraints on the velocity-weighted cross section for DM self-annihilation as a function of the DM particle mass.

• The paper presents a combined dark matter search using data from five gamma-ray observatories to set stringent limits on DM annihilation cross sections in dwarf spheroidal galaxies.
• The study employs a unified likelihood framework that standardizes astrophysical inputs and annihilation channels, enhancing the robustness of DM detection efforts.
• Results improve sensitivity by excluding thermal relic cross sections for DM particles below 100–150 GeV, underscoring the value of multinational collaboration in astrophysics.

Combined Dark Matter Searches Towards Dwarf Spheroidal Galaxies

The paper entitled "Combined Dark Matter searches towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, HESS, MAGIC and VERITAS" presents a significant advancement in the search for dark matter (DM) through indirect detection methods. This collaborative effort fuses data from an array of sophisticated observational instruments, namely Fermi-LAT, HAWC, HESS, MAGIC, and VERITAS, to enhance the sensitivity and robustness of searches for DM in dwarf spheroidal galaxies (dSphs).

Motivation and Methodology

The search for DM is driven by its potential to illuminate physics beyond the Standard Model. Indirect detection of DM relies on observing the standard model annihilation products, typically gamma rays, in regions of high DM density such as dSphs. These galaxies are characterized by their substantial DM content and low astrophysical backgrounds, making them ideal targets for such studies.

The researchers employ a consortium-based approach wherein each participating experiment pre-processes its individual dataset to maintain confidentiality over raw data while still allowing for analysis at the likelihood level. A unified framework is adopted, involving:

• Consistent handling of astrophysical factors (J-Factors) for each target.
• A standardized set of annihilation channels.
• Shared statistical methodologies and systematics management.

Instruments and Observations

Fermi-LAT, operational since 2008, captures high-energy gamma rays in the 20 MeV to 300 GeV range, leveraging its wide field of view to scan nearly the entire sky every few hours. HAWC, on the other hand, targets energies between 300 GeV and 100 TeV from its vantage point in Mexico, utilizing water Cherenkov detectors to pinpoint gamma-ray showers. The Imaging Atmospheric Cherenkov Telescopes (IACTs)—HESS, MAGIC, and VERITAS—enhance the detection spectrum up to 100 TeV (with variations per system), adding resolution from diverse geographical locations.

Results and Implications

The analysis culminated in upper limits on the velocity-weighted cross section for DM self-annihilation as a function of DM particle mass derived from observations of 20 dSphs. The combined data approach permits exclusion limits at the thermal relic cross section for DM particles with masses below 100 GeV annihilating into $b\bar{b}$ channel, and below 150 GeV in the $\tau^+ \tau^-$ channel, thereby demonstrating improved sensitivity over individual datasets.

This joint effort advances our capacity to detect DM by leveraging the statistical power and complementary strengths of multiple observational platforms. It underscores the potential of collaborative frameworks to push the boundaries of DM research. Future efforts could expand the number of observed dSphs and refine the models used in likelihood combinations, potentially uncovering new insights into the nature of DM.

Conclusion

This paper is a testament to the efficacy of multinational and multi-instrument collaborations in astrophysical research, particularly in the quest to understand dark matter. While no significant gamma-ray excess was detected, the constraints provided are invaluable to refining theoretical models. Moving forward, such collaborative ventures will be instrumental in uncovering the elusive properties of dark matter and enhancing our comprehension of the universe.