2009/03/31 by Doron Kushnir, Boaz Katz, Eli Waxman · 3 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Cluster (spacecraft) #Cosmic ray #Equipartition theorem #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Luminosity #Magnetic field #Physics #Radio galaxy #astro-ph.CO #astro-ph.HE
paper · pdf · doi:10.1088/1475-7516/2009/09/024
published as JCAP 0909:024,2009 · 7 pages, 2 figures, somewhat revised, published in JCAP
openalex publication_date 2009/09/18 · arxiv created 2010/02/22 · arxiv updated 2010/02/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We argue that the observed correlation between the radio luminosity and the thermal X-ray luminosity of radio emitting galaxy clusters implies that the radio emission is due to secondary electrons that are produced by p-p interactions and lose their energy by emitting synchrotron radiation in a strong magnetic field, B > (8π aT CMB 4 ) 1/2 ≃ 3 μG. We construct a simple model that naturally explains the correlation, and show that the observations provide stringent constraints on cluster magnetic fields and cosmic rays (CRs): Within the cores of clusters, the ratio β core between the CR energy (per logarithmic particle energy interval) and the thermal energy is β core ∼ 2 10 −4 ; The source of these CRs is most likely the cluster accretion shock, which is inferred to deposit in CRs ∼ 0.1 of the thermal energy it generates; The diffusion time of 100 GeV CRs over scales ≳ 100 kpc is not short compared to the Hubble time; Cluster magnetic fields are enhanced by mergers to ≳ 1% of equipartition, and decay (to < 1 μG) on 1 Gyr time scales. The inferred value of β core implies that high energy gamma-ray emission from secondaries at cluster cores will be difficult to detect with existing and planned instruments.