27-31 August 2018
LVH, Luisenstraße 58, 10117 Berlin
Europe/Berlin timezone
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Contribution Talk

-2- B. von Langenbeck

Detection of virial shocks in Fermi-LAT galaxy clusters


  • Mr. Ido REISS

Primary authors


Abstract content

Galaxy clusters are thought to grow by accreting mass through large scale, strong yet elusive, virial shocks. These collisionless shocks are thought to accelerate relativistic electrons, generating a spectrally-flat leptonic virial ring. However, with the exception of a VERITAS signal from the Coma cluster, attempts to detect virial rings have all failed. By stacking and rescaling Fermi-LAT data at 1-100GeV for the 112 most massive, high latitude, extended clusters we identify (at the 5.9 sigma confidence level) a bright, spectrally flat gamma-ray ring at the expected radius. This indicates that ~0.6% (with an uncertainty factor ~2) of the thermal energy is deposited in relativistic electrons over a Hubble time. This detection is confirmed using two multi messenger analyses of individual clusters: (1) A combined VERITAS (~220GeV), LAT and ROSAT R1 (~0.2keV) elliptical signal in Coma. (2) Planck SZ pressure near the virial radius, coincident with a LAT gamma-ray excess in Coma, A2319, and A2142. This results validate the shock paradigm, calibrate its parameters, and indicate that such shocks significantly contribute to the diffuse extragalactic gamma-ray and radio backgrounds.