Speaker
Description
As the largest gravitationally bound object in the Universe, galaxy clusters are favorable targets for indirect dark matter (DM) search. The GeV-TeV gamma-ray line is the smoking gun signal of the DM annihilation/decay. From the 15.5 years' observation data of the nearby massive galaxy clusters by Fermi-LAT, we detect a tentative gamma-ray line signal at ~43 GeV. The line signal has a net TS value of ~30 in the directions of Virgo, Fornax, and Ophiuchus clusters, three massive clusters with the highest J-factors expected to generate the dark matter annihilation signal. The signal still presents when the data of another 10 nearby massive clusters have also been included, though the TS value decreases to ~21 likely because of their lower signal-to-noise ratios. We correct for the ‘‘look elsewhere effect’’, the global significance of the signal is ~4.3σ and ~3.7σ for the samples of three clusters and 13 clusters, respectively. We further discuss potential systematic effects in this search. However, this signal is absent in the inner Galaxy, which disfavors both the instrumental effect and the canonical dark matter annihilation interpretation, and a more sophisticated dark matter model or very peculiar astrophysical scenario might be needed.