Distributions of the XRT 2−10 keV luminosity (lower axis) and flux (unabsorbed, upper axis) drawn from the light curves binned at 100 s. Top: SFXTs monitored for two years (Romano et al. 2011); the thin red histograms show the part of the data collected as outburst observations, thus including both the initial bright flare and the follow-up observations. Middle: SFXTs monitored for one year (J1841 in Romano et al. 2009); the thin red histograms show outburst observations collected outside of the monitoring campaign (one outburst per source). Bottom: SFXTs monitored for one orbital period (Romano et al. 2010; Ducci et al. 2013; Romano et al. 2012b). The sample size, N, is reported in each panel.