Stringent Constraints On The Dark Matter Annihilation Cross Section From Subhalo Searches With The Fermi Gamma-Ray Space Telescope

TL;DR

This study uses Fermi gamma-ray data and simulations to set stringent limits on dark matter annihilation cross sections, especially for particles below 200 GeV, by analyzing unidentified gamma-ray sources and their characteristics.

Contribution

The paper provides the strongest constraints to date on dark matter annihilation cross sections below 200 GeV using subhalo searches with Fermi data, improving upon previous limits from dwarf galaxies and the Galactic Center.

Findings

Limits on dark matter annihilation cross section are the most stringent below 200 GeV.

Unidentified gamma-ray sources are consistent with dark matter particles of 30-60 GeV or 8-10 GeV.

Four bright high-latitude sources have spectra compatible with specific dark matter annihilation models.

Abstract

The dark matter halo of the Milky Way is predicted to contain a very large number of smaller subhalos. As a result of the dark matter annihilations taking place within such objects, the most nearby and massive subhalos could appear as point-like or spatially extended gamma-ray sources, without observable counterparts at other wavelengths. In this paper, we use the results of the Aquarius simulation to predict the distribution of nearby subhalos, and compare this to the characteristics of the unidentified gamma-ray sources observed by the Fermi Gamma-Ray Space Telescope. Focusing on the brightest high latitude sources, we use this comparison to derive limits on the dark matter annihilation cross section. For dark matter particles lighter than ~200 GeV, the resulting limits are the strongest obtained to date, being modestly more stringent than those derived from observations of dwarf galaxies or the Galactic Center. We also derive independent limits based on the lack of unidentified gamma-ray sources with discernible spatial extension, but these limits are a factor of ~2-10 weaker than those based on point-like subhalos. Lastly, we note that four of the ten brightest high-latitude sources exhibit a similar spectral shape, consistent with 30-60 GeV dark matter particles annihilating to b quarks with an annihilation cross section on the order of sigma v ~ (5-10) x 10^-27 cm^3/s, or 8-10 GeV dark matter particles annihilating to taus with sigma v ~ (2.0-2.5) x 10^-27 cm^3/s.