Comparison of the fluxes [ph cm−2 s−1] in time bins obtained with the fitting pipeline keeping the spectral index fixed vs. letting the spectral index be free. The empty circles indicate results from analyses that did not converge, i.e., MINUIT Return Code q ≠ 0. MINUIT (James 1994) is the optimizer adopted in the likelihood analysis. The plot shows the fluxes measured for the quasar Ton 599. In this case, the fit for the highest-flux point (with TS ∼ 4) converged when the spectral index was set free, but did not converge when the spectral index was fixed.