To estimate the robustness of the different methods, we repeated each simulation a thousand times. The resulting flux errors for the three Gaussian components were evaluated. The histograms show the error distribution for the two cases, left (right) panels without (with) SW. The upper row shows the results for the method described in Sect. 3.2 using only Off positions to estimate T_cal/T_sys. The middle panels were produced using the procedure from Sect. 3.3. The lower row contains the result for the classical method (T_sys = const. and T_cal = const.). The bin width has been kept constant for each histogram, such that the amplitudes can be directly compared. For each distribution of errors, we fitted a Gaussian distribution, the parameters (mean value μ and width σ) of which are stated in the plots.