Detailed study of extended gamma-ray morphology in the vicinity of the Coma cluster with Fermi-LAT

Context. Galaxy clusters can be sources of high energy (HE) $\gamma$-ray radiation due to the efficient acceleration of particles up to the highest energies. Up to now, the only candidate of emitting $\gamma$-rays is the Coma cluster, towards which there is an excess of the $\gamma$-ray emission detected by the Fermi Large Area Telescope (LAT). Aims. In particular, we aim to understand the origin of this excess and its connection with the Coma cluster. Methods. Using $\mathrm{\sim12.3}$ years of Fermi-LAT data, we analysed the region of the Coma cluster between energies 100 MeV and 1 TeV by detailed spectral and morphological analysis. Results. We detected a diffuse $\gamma$-ray emission between 100 MeV and 1 TeV energies in the region of the Coma cluster with $5.4\sigma$ extension significance and 68% containment radius of $0.82^{+0.1}_{-0.05}$ degrees derived with a 2D homogeneous disk model. The corresponding $\gamma$-ray spectrum extends up to $\sim50$ GeV with power-law spectral index $\mathrm{\Gamma=2.23\pm0.11}$ and energy flux of $\mathrm{(3.48\pm0.68)\times10^{-12}\,erg\,cm^{-2}\,s^{-1}}$. Besides, we also found that three point-like sources in the background with power-law indexes of $\mathrm{2.44\pm0.28}$, $\mathrm{2.56\pm0.32}$, and $\mathrm{1.99\pm0.30}$ show improvement in the fit by $\mathrm{\Delta_{AIC}}=-7.2$. Conclusions. We suggest that the observed $\gamma$-ray emission can be produced within the Coma cluster since the contribution from the background AGNs and star-forming galaxies is not sufficient to provide the observed total $\gamma$-ray luminosity and the morphology. However, to confirm this suggestion, we need more data because of the low statistics of each component in the model.