Coincident Sunyaev-Zel'dovich and Gamma-Ray Signals from Cluster Virial Shocks

Virial shocks around galaxy clusters are expected to show a cutoff in the thermal Sunyaev-Zel'dovich (SZ) signal, coincident with a leptonic ring. However, until now, leptonic virial signals have only been reported in Coma and in stacked Fermi Large Area Telescope (LAT) clusters, and an SZ viri...

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Bibliographic Details
Published in:The Astrophysical journal 2020-05, Vol.895 (1), p.72
Main Authors: Keshet, Uri, Reiss, Ido, Hurier, Guillaume
Format: Article
Language:English
Subjects:
Galaxy clusters
Gamma-rays
Non-thermal radiation sources
Shocks
Sunyaev-Zeldovich effect
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Summary:Virial shocks around galaxy clusters are expected to show a cutoff in the thermal Sunyaev-Zel'dovich (SZ) signal, coincident with a leptonic ring. However, until now, leptonic virial signals have only been reported in Coma and in stacked Fermi Large Area Telescope (LAT) clusters, and an SZ virial shock signal reported only in A2319. We point out that a few clusters-presently Coma, A2319, and A2142-already show a significant ( ) sharp drop in the Planck y parameter near the virial radius, coincident with a (2.2 -3.9 ) LAT γ-ray excess. These signatures are naturally interpreted as tracers of the virial shocks of these clusters, at joint medium to high confidence levels. The electron acceleration rates inferred from the γ-rays are consistent with previous measurements. The combined signal, along with galaxy count data, allows a separate measurement of the ∼0.5% (with a factor of ∼2 uncertainty) acceleration efficiency and of the accretion rate. Lower limits on order of a few are imposed on the shock Mach numbers.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab8c49