Detection of quasi-periodic oscillations in the long-term radio light curves of the blazar OT 081

Abstract

We report the detection of quasi-periodic oscillations (QPOs) in the radio light curves at 4.8, 8 and 14.5 GHz of the blazar OT 081, by means of the Weighted Wavelet Z-transform(WWZ) and Lomb-Scargle periodogram (LSP) methods. The LSP diagrams and time-averaged WWZ powers demonstrate several significant claims of QPOs above the 4σ confidence level: QPOs of ∼850 and ∼1500 days in the 4.8-GHz light curve, ∼850, ∼1120 and ∼1540 days in the 8-GHz light curve, ∼850 and ∼1130 days in the 14.5-GHz light curve. The Keplerian orbit parameters in a binary black hole system have been estimated, assuming the QPO of ∼850 days appearing in all three wavebands is a real periodicity. Moreover, a pure geometrical scenario with blobs moving helically inside the jet provides another plausible explanation for the detected QPOs.

Quasiperiodic Behavior in the γ-Ray Light Curve of the Blazar PKS 0405-385

“…Through the above three formulas, the fractional variability amplitude values of γ-ray and G band are F γ = 0.59 ± 0.02 and F G = 0.58 ± 0.02, respectively, which indicates that there is relatively significant variability in this case. Recently, Li et al (2021) reported that there might be a positive correlation between F var and frequency, but this phenomenon is not apparent here.…”

“…Alternatively, QPO-like flux modulations might be related to a geometrical scenario with the relativistic motion of the enhanced emission (or blobs) along the helical path of a jet. This scenario has been invoked to explain QPOs in PKS 2247-131 (Zhou et al 2018), 3C 454.3 (Sarkar et al 2021, and OT 081 (Li et al 2021) recently. When the emitting blob is moving helically within the magnetized jet with a high bulk Lorentz factor (Γ), due to the relativistic effects, the periodic changes in the viewing angle θ cause the Doppler boosted emission to be periodically modulated.…”

“…In the radio domain, a QPO signal (∼176 days) with 21 cycles was announced in J0849+5108 (Zhang & Wang 2021). In the same year, Li et al (2021) found about 850 days of periodic modulation in all three bands (4.8, 8, and 14.5 GHz) of the BL Lac OT 081, and a pure geometric scenario provided a plausible explanation for the detected QPO. Interestingly, a QPO of ∼4.69 yr (>5σ confidence level) was found in PKS J2134-0153, in which the 15 GHz light curve is very close to sinusoidal variation (Ren et al 2021a).…”

“…Quasiperiodic variability is one of the blazar's light curve characteristics. Furthermore, studies of the quasiperiodic oscillation (QPOs) of blazars allow us to explore the central engine's structures, physical properties, dynamics, and radiation mechanisms, although QPOs are rare and transient in their multiwavelength light curves (Li et al 2021). When searching for sources with QPO behavior, false periodic events may occur if the number of cycles is too small.…”

Alterations in Multi-channel EEG Dynamics During a Stressful Shooting Task in Virtual Reality Systems

“…We note that a common approach to derive PSDs of an unevenly sampled time series is the Lomb-Scargle periodogram (LSP; Lomb 1976;Scargle 1982), which is also frequently used in the literature (Rani et al 2009(Rani et al , 2010Bhatta et al 2016b;Sandrinelli et al 2016;Castignani et al 2017;Sandrinelli et al 2017;Gaur et al 2018;Gupta et al 2019;Żywucka et al 2020;Bhatta & Dhital 2020;Li et al 2021). However, with numerical simulation, we demonstrate in Appendix C that the LSP method does not reproduce the shape of the underlying power spectrum correctly down to the highest frequencies.…”