Search for a gamma-ray line feature from a group of nearby galaxy clusters with Fermi LAT Pass 8 data

Abstract

Galaxy clusters are the largest gravitationally bound objects in the Universe and may be suitable targets for indirect dark matter searches. With 85 months of Fermi LAT Pass 8 publicly available data, we analyze the gamma-ray emission in the direction of 16 nearby galaxy clusters with an unbinned likelihood analysis. No statistically or globally significant $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{ray}$ line feature is identified and a tentative line signal may present at $\ensuremath{\sim}43\text{ }\text{ }\mathrm{GeV}$. The 95% confidence level upper limits on the velocity-averaged cross section of dark matter particles annihilating into double $\ensuremath{\gamma}$ rays (i.e., $⟨\ensuremath{\sigma}v{⟩}_{\ensuremath{\chi}\ensuremath{\chi}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}}$) are derived. Unless very optimistic boost factors of dark matter annihilation in these galaxy clusters have been assumed, such constraints are much weaker than the bounds set by the Galactic $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{ray}$ data.