Peak flux detection threshold as a function of the simulated flare duration, reported as FWHM. Triangles (squares): flux threshold is defined as the peak flux for which half (20%) of the simulated flares are detected. The observing period is 7.25 yr, E > 0.3 GeV. The extraction radius corresponds to the containment radius for 68% of events. Open squares and triangles refers to a faint source (giving a total number of counts on Fermi-LAT that is 20% of the background counts within the scrutinized period). Filled symbols refer to a bright source (corresponding to the case of 3C 454.3). Curves refer to sensitivities calculated assuming constant exposure, hat shaped flares, for (e.g. 99.87%c.l.).