Bundle of power-law spectra, F(ν) ∝ ν^− α, with α = 1.1, 1.22, 1.4, 1.55, 1.7 normalized to the flux of the radio halo derived from Brown & Rudnick (2011) WSRT data using an aperture radius R_H = 0.85   R₅₀₀. Models are corrected for the SZ-decrement (F_obs(ν,Ω_H) = F(ν,Ω_H) + δF_SZ(ν,Ω_H), Sect. 2) measured on the same aperture radius. The observed high-frequency points are taken from T03.