Comparison between the photon index obtained in the spectral fit (see Sect. 3.2; Γ_fit, data), which was then simulated and fit again (Γ_fit, simul). From top to bottom: results for SS02, SS04, SS07, and SS10 are shown. Error bars for Γ_fit, simul are shown (16th−84th percentiles), whereas we show uncertainties (16th−84th percentiles) in Γ_fit, data around the 1:1 relation. We colour coded data with the ratio between the total (source plus background) and background-only 10 − 25 keV count rates (see white and grey symbols in the top panel of Fig. 3).