Optical microvariability in Active Galactic Nuclei: Truth, post-truth, and statistics

CELLONE, S. A.

Córdoba

Encuentro; 8th Friends of Friends Meeting - Linking astronomy and friends in Córdoba; 2018

OAC-IATE

It is a fact that Active Galactic Nuclei (AGN) display variable emission along the whole electromagnetic spectrum.  Different AGN classes and subclasses, in turn, are characterised by different amplitudes, duty-cycles, and time-scales in their light-curves. While jetted AGN are in general more variable than their non-jetted counterparts, those within the blazar class show the most extreme behaviours.  Optical microvariability (i.e., significant flux variations on hours/minutes time-scales), in particular, has been used as a powerful tool to test processes taking place in the innermost regions of AGN jets.Systematic uncertainties affecting ground-based optical observations, however, have led in the past to questionable claims of extreme microvariability events. Moreover, and rather surprisingly, these observational limitations have challenged our efforts to establish a firm and reliable criterion to detect and quantify microvariability.I will review here some results from studies of optical microvariability in AGN, carried out by our group at FCAG/IALP and IAR along the last several years. Particular attention will be paid to the influence of AGN host galaxies on photo-polarimetric observations, and to the evaluation and re-assessment of statistical tests usually applied to detect microvariability in optical light-curves.