In black: cross-correlation power spectrum between the RASS in the 0.5−2.0 keV energy band map and the MILCA y-map computed from Planck data. As a dark blue solid line we show the theoretical one-halo tSZ-Xray cross-correlation power spectrum for Planck best-fitting cosmological parameters, in red the contribution of the two-halo term, and as dashed lines we show the 1σ uncertainties on the theoretical prediction as estimated in Hurier et al. (2014). Uncertainties have been computed as presented in Eq. (15).