Search for dark matter annihilation signals from UFOs with H.E.S.S

TL;DR

This study used H.E.S.S. gamma-ray observations to search for dark matter annihilation signals from unidentified Fermi-LAT objects, setting constraints on dark matter models and challenging their ability to explain these sources.

Contribution

First to systematically analyze H.E.S.S. data for dark matter signals from UFOs, deriving new constraints on annihilation cross-sections and J-factors for TeV-scale dark matter.

Findings

No significant gamma-ray emission detected from UFOs.

Constraints placed on dark matter annihilation cross-section and J-factors.

Models with dark matter mass > 0.3 TeV are marginally compatible with UFO emissions.

Abstract

Cosmological N-body simulations show that Milky-Way-sized galaxies harbor a population of unmerged dark matter subhalos. These subhalos could shine in gamma rays and be eventually detected in gamma-ray surveys as unidentified sources. We search for very-high-energy (VHE, $E\geq 100$ GeV) gamma-ray emission using H.E.S.S. observations carried out from a thorough selection of unidentified Fermi-LAT Objects (UFOs) as dark matter subhalo candidates. Provided that the dark matter mass is higher than a few hundred GeV, the emission of the UFOs can be well described by dark matter annihilation models. No significant VHE gamma-ray emission is detected in any UFO dataset nor in their combination. We, therefore, derive constraints on the product of the velocity-weighted annihilation cross-section $\langle \sigma v\rangle$ by the $J$-factor on dark matter models describing the UFO emissions. Upper limits at 95% confidence level are derived on $\langle \sigma v\rangle J$ in $W^+W^-$ and $\tau^+\tau^-$ annihilation channels for the TeV dark matter particles. Focusing on thermal WIMPs, strong constraints on the $J$-factors are obtained from H.E.S.S. observations. Adopting model-dependent predictions from cosmological N-body simulations on the $J$-factor distribution function for Milky Way (MW)-sized galaxies, only $\lesssim 0.3$ TeV mass dark matter models marginally allow to explain observed UFO emission.