Spectral energy distribution of Phoenix cluster. The black dots show data obtained from literature. The red dots show data presented in this work. The best-fit spectral index through the data is −1.12 ± 0.02. A curvature term is included in the fit, but is found to be negligible. The data point at 220 GHz is excluded from the fit as free-free and thermal dust emissions are expected to contribute significantly at this frequency.