NGC 4151 variance spectrum, similar to Fig. 1. The black points are calculated from light curve segments with duration T_max = 3 days, while the red point with T_max = 12 days. The blue line shows the best-fit variance model calculated with T_max = 3. The slope of the best-fit black dashed line is b = −2.6 ± 0.4. The best-fit variance model for this source includes host galaxy absorption with E(B − V) = 0.35 (see Sect. 6.5 for more details). Grey points and solid black line as in Fig. 1.