A team analyzing Fermi Large Area Telescope (LAT) gamma-ray data reports a set of narrow spectral lines near 70, 40 and 13 GeV that appear when the gamma rays are cross-correlated with X‑ray maps or when many galaxy clusters are stacked. The pattern of lines matches the energies expected if a roughly 70 GeV weakly interacting massive particle (WIMP) annihilates into two photons (γγ) or into a photon plus a Z or Higgs boson (γZ, γh). The strongest statistical signal comes from cross-correlation with eROSITA X‑ray maps, with a trial‑corrected global significance up to 5.6σ; the plain stacking analysis reaches about 2.3σ.

To look for faint, narrow features the researchers combined many independent approaches. They used about 16.3 years of archival Fermi‑LAT Pass‑8 ULTRACLEANVETO data and focused on photons between roughly 3 and 100 GeV, binned finely to keep the LAT energy resolution. They suppressed foregrounds by aggressively masking known gamma‑ray sources from the 4FGL‑DR4 catalog and the Galactic plane. Two analysis routes were used: cross‑correlating the gamma rays with eROSITA X‑ray maps as a tracer of large‑scale structure, and stacking gamma rays at the three‑dimensional positions (including redshift) of clusters in the MCXC, eROSITA and DESI catalogs. Narrow spectral filters, calibrated with Monte Carlo simulations, were applied to detect single lines and constrained line complexes.

When translated into particle physics, the detected lines fit a set of channels expected from WIMP annihilation. The paper reports intrinsic channel cross‑sections of order 10^(-20) to 10^(-19) cm^3 s^(-1) and finds high‑resolution spectra that resolve six lines plus a broader three‑line feature. Those features are said to align naturally with the nine channels expected if two WIMP species cross‑annihilate, with profile‑likelihood masses 67.3 (+0.1/−0.1) GeV and 71.4 (+0.2/−0.1) GeV. The authors quote combined statistical evidence at the level of about 5.3σ after profiling, and state that the Galactic‑center GeV excess is broadly consistent with the expected continuum from χχ→b b̄ for this scenario.