Detection of virial shocks in stacked Fermi-LAT clusters

Understand

Galaxy clusters are thought to grow by accreting mass through large-scale, strong, yet elusive, virial shocks.

• Such a shock is expected to accelerate relativistic electrons, thus generating a spectrally-flat leptonic virial-ring.
• However, until now, only the nearby Coma cluster has shown evidence for a $\gamma$-ray virial ring.
• We stack Fermi-LAT data for the 112 most massive, high latitude, extended clusters, enhancing the ring sensitivity by rescaling clusters to their virial radii and utilizing the expected flat energy spectrum.