Abstract:
The incidence of intranight optical variability (INOV) is known to differ significantly among
different classes of powerful active galactic nuclei (AGN). A number of statistical methods
have been employed in the literature for testing the presence of INOV in the light curves,
sometimes leading to discordant results. In this paper, we compare the INOV characteristics
of six prominent classes of AGN, as evaluated using three commonly used statistical tests,
namely the χ² -test, the modified C-test and the F-test, which has recently begun to gain
popularity. The AGN classes considered are: radio-quiet quasars, radio-intermediate quasars,
lobe-dominated quasars, low optical polarization core-dominated quasars, high optical polar-
ization core-dominated quasars and TeV blazars. Our analysis is based on a large body of
AGN monitoring data, involving 262 sessions of intranight monitoring of a total 77 AGN,
using 1–2 m class optical telescopes located in India. In order to compare the usefulness of the
statistical tests, we have also subjected them to a ‘sanity check’ by comparing the number of
false positives yielded by each test with the corresponding statistical prediction. The present
analysis is intended to serve as a benchmark for future INOV studies of AGN of different
classes.
