A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope

TL;DR

This paper reports an improved search for gamma-ray lines in Fermi LAT data, finding a 3.2 sigma excess at 130 GeV near the Galactic center, which could indicate dark matter annihilation.

Contribution

The study introduces a new data-driven method for selecting target regions and updates the analysis with 43 months of data, revealing a potential dark matter signal.

Findings

A 4.6 sigma indication for a gamma-ray line at 130 GeV near the Galactic center.

The observed excess corresponds to a dark matter particle mass of about 130 GeV.

Estimated dark matter annihilation cross-section is approximately 1.27 x 10^-27 cm^3 s^-1.

Abstract

The observation of a gamma-ray line in the cosmic-ray fluxes would be a smoking-gun signature for dark matter annihilation or decay in the Universe. We present an improved search for such signatures in the data of the Fermi Large Area Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides updating to 43 months of data, we use a new data-driven technique to select optimized target regions depending on the profile of the Galactic dark matter halo. In regions close to the Galactic center, we find a 4.6 sigma indication for a gamma-ray line at 130 GeV. When taking into account the look-elsewhere effect the significance of the observed excess is 3.2 sigma. If interpreted in terms of dark matter particles annihilating into a photon pair, the observations imply a dark matter mass of 129.8\pm2.4^{+7}_{-13} GeV and a partial annihilation cross-section of <\sigma v> = 1.27\pm0.32^{+0.18}_{-0.28} x 10^-27 cm^3 s^-1 when using the Einasto dark matter profile. The evidence for the signal is based on about 50 photons; it will take a few years of additional data to clarify its existence.