10.12.3 Calibration models

The short-timescale candidate selection criteria are based on the variogram analysis (see Section 10.12.4), with thresholds calibrated by cross-matched catalogues of known variable (including both short and longer timescales) and constant stars, from OGLE catalogues (Udalski et al. 1992).

The variogram analysis defines a detection threshold ${\gamma }_{\det }$ that can be compared to the variogram values of each investigated source. This threshold corresponds to the level of variability above which the observed variability is considered as not spurious. For objects with mean $G$ fainter than 16 mag, a magnitude-dependent detection threshold is defined based on the variogram analysis of cross-matched sources and on the simulation work done previously to assess the power of the variogram method for short-timescale variability detection with Gaia (see Roelens et al. 2017). For brighter objects, a constant threshold was employed, which was equal to the one adopted for the mean $G$ of 16 mag.