A Universal 1.5 GeV Gamma-Ray Line in Active Galactic Nuclei

TL;DR

A 1.5 GeV gamma-ray line was detected in three active galactic nuclei, with a significance above 5 sigma, potentially indicating dark matter annihilation rather than standard astrophysical processes.

Contribution

This is the first report of a consistent gamma-ray spectral line at 1.5 GeV across multiple AGN, challenging existing emission models and suggesting a possible dark matter origin.

Findings

Line detected with >5 sigma significance in combined analysis.

Line flux remains stable over 17 years of observations.

Spectral feature inconsistent with standard jet emission mechanisms.

Abstract

We report the detection of a gamma-ray spectral line at approximately 1.5 GeV in three active galactic nuclei (AGN) using 17 years of Fermi-LAT observations. The sample includes both blazars (with relativistic jets directed toward Earth) and a radio galaxy (with a misaligned jet, free from significant beaming effects). The line is detected with local significances of $\sim$4.1$\sigma$, $\sim$3.9$\sigma$, and $\sim$2.8$\sigma$ in the individual sources. A joint likelihood analysis yields a combined test statistic TS $\simeq$ 57.77, corresponding to a significance well above 5$\sigma$. The line flux remains stable over the full observation period, in contrast to the variable continuum emission from the AGN. The appearance of an identical spectral feature in astrophysically distinct environments is difficult to reconcile with standard jet-based emission mechanisms. While a conventional astrophysical explanation remains elusive, the signal's characteristics are consistent with predictions for dark matter annihilation. This finding motivates further investigation into the nature of this spectral feature and its possible connection to particle dark matter.