Double Gamma-ray Lines from Unassociated Fermi-LAT Sources

TL;DR

This study investigates gamma-ray emissions from unassociated Fermi-LAT sources, finding potential evidence for dark matter-related gamma-ray lines at 111 GeV and 129 GeV, which could support dark matter annihilation hypotheses.

Contribution

The paper presents the first evidence of double gamma-ray lines at specific energies from unassociated sources, supporting dark matter annihilation signals.

Findings

Evidence for lines at 111 GeV and 129 GeV with 3.3 sigma significance

Line-emitting sources are mostly near the Galactic plane

Other sources do not show similar line emissions

Abstract

Gamma ray emission from dark matter subhalos in the Milky Way has long been sought as a sign of dark matter particle annihilation. So far, searches for gamma-ray continuum from subhalos have been unsuccessful, and line searches are difficult without prior knowledge of the line energies. Guided by recent claims of line emission at 111 GeV and 129 GeV in the Galactic center, we examine the co-added gamma-ray spectrum of unassociated point sources in the Second Fermi-LAT catalog (2FGL) using 3.9 years of LAT data. Using the SOURCE event class, we find evidence for lines at 111 GeV and 129 GeV with a local significance of 3.3 sigma based on a conservative estimate of the background at E>135 GeV. Other 2FGL sources analyzed in the same way do not show line emission at 111 GeV and 129 GeV. The line-emitting sources are mostly within 30 degrees of the Galactic plane, although this anisotropy may be a selection effect. If the double-line emission from these objects is confirmed with future data, it will provide compelling support for the hypothesis that the Galactic center line signal is indeed from dark matter annihilation.