A1 Refereed original research article in a scientific journal
Radio and gamma-Ray Variability in Blazar S5 0716+714: A Year-like Quasi-periodic Oscillation in the Radio Light Curve
Authors: Li Xiao-Pan, Yang Hai-Yan, Cai Yan, Lähteenmäki Anne, Tornikoski Merja, Tammi Joni, Suutarinen Sofia, Yang Hai-Tao, Luo Yu-Hui, Wang Li-Sha
Publisher: IOP Publishing Ltd
Publication year: 2023
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Article number: 157
Volume: 943
Number of pages: 9
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/acae8c
Web address : https://doi.org/10.3847/1538-4357/acae8c
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/178966415
The nearly 33 yr long-term radio light curve obtained with the Metsahovi Radio Observatory 14 m telescope at 37 GHz and the recent 12.7 yr gamma-ray light curve of the blazar S5 0716+714 at 0.1-300 GeV from the Fermi Large Area Telescope (Fermi-LAT) were analyzed by using the Lomb-Scargle periodogram and the weighted wavelet Z-transform techniques. In the radio light curve, we discovered a possible quasi-periodic oscillation (QPO) signal of about 352 +/- 23 days at a confidence level of similar to 3 sigma. We recalculated the periodicity and its significance in a chosen time range that has higher variability and denser sampling, and then found that the significance had increased to a confidence level of 99.996% (∼ 4.1σ). This QPO component was further confirmed by fitting a linear autoregressive integrated moving average model to the selected radio light curve. A possible QPO of 960 +/- 80 days at a 99.35% level (∼ 2.7σ) was found in the gamma-ray light curve, which generally agrees with the earlier QPO claims of S5 0716+714. This paper discusses possible mechanisms for this potential year-like QPO. One possibility is a pure geometrical scenario with blobs moving helically inside the jet. Another is a supermassive binary black hole involving a gravitational wave-driven regime. In the latter scenario, we derived a milliparsec separation in the binary system that undergoes coalescence within a century due to the emission of low-frequency gravitational waves.
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