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

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 gamma-ray line feature is identified and a tentative line signal may present at similar to 43 GeV. The 95% confidence level upper limits on the velocity-averaged cross section of dark matter particles annihilating into double gamma rays (i.e., sigma nu (chi chi -> gamma 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 gamma-ray data.