Spectrum of the radio halo extracted within an aperture of 17.5′ (red, 0.37 R₅₀₀) and 13′ (blue, 0.27 R₅₀₀). The high-frequency points are corrected for the SZ-decrement measured on the same scales. For comparison the empty symbols mark fluxes measured in the same aperture radius using the Brown & Rudnick (2011) data. Best fits to the low-frequency data are reported as solid lines (same color-code), while the best fit to the T03 compilation (dashed line) and the synchrotron model with the cut-off of Fig. 1 (dot-dashed line) are reported for comparison.