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 $\mathrm{d}\mathrm{e}{\mathrm{g}}^2$ 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 $3\sigma$. The best-fit dark matter mass and annihilation cross-section for this cluster are equal to $(60.0\pm 11.8)$ GeV and $⟨\sigma v⟩=(6.0\pm 0.6)\times {10}^{-25}\mathrm{c}{\mathrm{m}}^3{\mathrm{s}}^{-1}$ for the $\bar{b}b$ 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 $2-2.5\sigma$, whereas all the remaining clusters show null results. The most stringent 95% c.l. upper limit for the WIMP annihilation cross-section among all the clusters is from SPT-CL J0455-4159, viz. $⟨\sigma v⟩=6.44\times {10}^{-26}{\text{cm}}^3{\text{s}}^{-1}$ for $m_{\chi }=10$ GeV and $b\bar{b}$ annihilation channel.