Search for Dark Matter Annihilation to gamma-rays from SPT-SZ selected Galaxy Clusters

We search for dark matter annihilation from galaxy clusters in the energy range from 1-300 GeV using nearly 16 years of Fermi-LAT data. For this purpose, we use 350 galaxy clusters selected from the 2500 deg² SPT-SZ survey. We model the dark matter distribution using the NFW profile for the main halo along with the Einasto profile for the substructure. The largest signal is seen for the cluster SPT-CL J2021-5257 with a significance of around 3σ. The best-fit dark matter mass and annihilation cross-section for this cluster are equal to (64.0 ± 11.8) GeV and σ v = (6.0 ± 0.6) × 10⁻²⁵ cm³ s⁻¹ for the b̄ b annihilation channel. However, this central estimate is in conflict with the limits on annihilation cross-section from dwarf spheroidal galaxies and hence cannot be attributed to dark matter annihilation. Three other clusters show significance between 2-2.5σ, whereas all the remaining clusters show null results. The most stringent 95% c.l. upper limit, which we obtain among the clusters with significance >2σ is from SPT-CL J2300-5331, given by σ v = 9 × 10⁻²⁶ cm³ s⁻¹ for a dark matter mass of 10 GeV corresponding to the bb̄ annihilation channel.