Comparing optical variability of type 1 and type 2 AGN from the BAT 9-month sample using ASAS-SN and TESS surveys

Abstract

We present an optical variability analysis and comparison of the samples of Seyfert 1 (Sy1) and Seyfert 2 (Sy2) galaxies, selected from the Swift 9 month BAT catalog, using the light curves from Transiting Exoplanet Survey Satellite (TESS) and All-Sky Automated Survey for SuperNovae (ASAS-SN). We measured the normalized excess variance of TESS and ASAS-SN light curves for each target and performed a Kolmogorov–Smirnov test between the two samples, where our results showed significant differences. This is consistent with predictions from the unification model, where Seyfert 2s are obscured by the larger scale dust torus and their variability is suppressed. This variability difference is independent of the luminosity, Eddington ratio, or black hole mass, further supporting geometrical unification models. We searched the dependence of the normalized excess variance of Sy1s on absolute magnitudes, Eddington ratio, and black hole mass, where our results are consistent with relations found in the literature. Finally, a small subsample of changing-look (CL) active galactic nuclei (AGNs) that transitioned during the time frame of the ASAS-SN light curves, with their variability amplitudes changing according to the classification, have larger variability as type 1s and smaller as 2s. The change of variability amplitudes can be used to better pinpoint when the type transition occurred. The consistency trend of the variability amplitude differences between Sy1s and Sy2s and between CL AGNs in 1 or 2 stages suggests that variability can be a key factor in shedding light on the CL AGN or the dichotomy between Sy1 or Sy2 populations.

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