H.E.S.S. spectrum of the source extracted from the complete data set. The differential flux points (with an excess significance of 1σ) and the 68% confidence band for the best fit are shown in the upper panel, as a function of true energy. The arrow represents an upper limit at the 99% confidence level. The residuals of the maximum likelihood fit are given in the lower panel as a function of the reconstructed energy, together with a fit of a constant (dashed line).