Microvariability in AGNs: study of different statistical methods – II. Light curves from simulated images

ZIBECCHI, L; ANDRUCHOW, I; CELLONE, S A; CARPINTERO, D D

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2020 vol. 498 p. 3013 - 3022

0035-8711

In a previous paper, we studied two statistical methods used to analyse the variability of active galactic nuclei (AGNs): the C andF statistics. Applying them to observed differential light curves (DLCs) of 39 AGNs, we found that, even though the C criterioncannot be considered as an actual statistical test, it could still be a useful parameter to detect variability, whereas F is a gooddetector of non-variability. In order to test these results under controlled input conditions, so that the different error sources couldbe individually evaluated, we generated a series of synthetic DLCs simulating astronomical images with different atmosphericconditions, such as cloud cover, seeing or sky brightness, as well as several types of intrinsic variability of the AGN, all with aspecific instrumental configuration. Having obtained light curves for each case, we applied both statistics to them in order to testtheir reliability. We found that a weight factor should always be used with these indices. The F-test has a tendency to classifynoisy non-variable curves as variable (i.e. false positives), although it is reliable and robust to correctly classify non-variablecurves. In contrast, although the C index tends to give false negatives, we found that whenever the C index indicates a source tobe variable, it effectively is. Finally, light curves with low amplitude variabilities are more likely to be affected by changes inatmospheric conditions.