Left: Map of the observed surface brightness decrement in the cluster centre from SRT data at 18.6 GHz. The profile reported on the right was obtained by blanking the radio sources and tracing annuli around the centre of the cluster, at intervals of a half-beam radius from one another. The blue arrow marks a localised surface-brightness excess in the south-eastern region. Right: Observed average surface brightness on annuli around the centre of the cluster, in blue. The continuous line shows the fit of the SZ decrement referred to the models from Eqs. (2) and (4).