Oscillatory patterns in the light curves of five long-term monitored type 1 active galactic nuclei

Abstract

A new combined data of 5 well known type 1 AGN are probed with a novel hybrid method in a search for oscillatory behavior. Additional analysis of artificial light curves obtained from the coupled oscillatory models gives confirmation for detected periods that could have physical background. We find periodic variations in the long-term light curves of 3C 390.3, NGC 4151, NGC 5548 and E1821+643, with correlation coefficients larger than 0.6. We show that oscillatory patterns of two binary black hole candidates NGC 5548 and E1821+643 corresponds to qualitatively different dynamical regimes of chaos and stability, respectively. We demonstrate that absence of oscillatory patterns in Arp 102B could be due to a weak coupling between oscillatory mechanisms. This is the first good evidence that 3C 390.3 and Arp 102B, categorized as double-peaked Balmer line objects, have qualitative different dynamics. Our analysis shows a novelty in the oscillatory dynamical patterns of the light curves of these type 1 AGN.

Two-dimensional correlation analysis of periodicity in active galactic nuclei time series

“…We perturbed both signals with red noise (see right panels) so that the original signal patterns are no longer able to be recognized. Precise mathematical description of red noise corruption of a signal is given in Kovačević et al (2018) In a recent study of CL AGN NGC 3516 (Shapovalova et al 2019), authors applied Lomb Scargle periodogram in order to detect periodicity in observed light curves of this object. However, potential periodic signals were of small significance.…”

“…Here we recapitulate key aspects of our hybrid method, which is discussed in details in Kovačević et al (2018). A conversion of set of light curves to 2D correlation maps is rel- diagonal positions represent the simultaneous change in signals at two different periods.…”

“…Nevertheless, in recent years an increasing number of reports on AGN periodicities have been published (see e.g. Graham et al 2015a,b;Liu et al 2016;Charisi et al 2016;Kovačević et al 2018;Li et al 2019;Kovačević et al 2019), suggesting that supermassive binary black holes might be detected through periodicity of their observed time series i.e. light curves, (see Barack et al 2019, and references therein).…”

“…However, the Fourier transform, the wavelet transform and related period estimation techniques can not tell about the presence of coordinated or independent changes among signals, as well as about relative directions of signal intensity variations. Our hybrid method based on two-dimensional (2D) correlation analysis were devised to deal with above issues (Kovačević et al 2018).…”

“…CL AGNs are objects showing the dramatic variability of the emission line profiles and the change of classification type within very short time interval (from days to years). Periodical variability has been discussed for some well-known CL AGN such as NGC 4151 (see Bon et al 2012;Kovačević et al 2018), NGC 5548 (see Bon et al 2016;Kovačević et al 2018) within the context of supermassive binary black hole candidate and pointed out as possibility for typical CL AGN NGC 2617 (see Oknyansky et al 2018). It would be interesting to know if CL AGN variability is periodic, since it can be a consequence of tidal disruption events (Xiang-Gruess et al 2016) or recoiling supermassive black hole (Kim et al 2018).…”