Using the Lomb–Scargle periodogram and the weighted wavelet Z-transform techniques, we have searched for quasi-periodic oscillations (QPOs) of the BL Lacertae object (BL Lac), PKS J2134–0153, in the 15-GHz radio light curve announced by the Owens Valley Radio Observatory 40-m telescope during the period from 2008 January 5 to 2019 May 18. This is the first time that the search for periodic radio signals in the BL Lac PKS J2134–0153 has used these two methods, which consistently reveal a QPO of 4.69 ± 0.14 yr (>5σ confidence level). We discuss possible causes for this QPO, and we expect that the binary black hole scenario, where the QPO is caused by the precession of a binary black hole, is the most likely explanation. Thus, the BL Lac PKS J2134–0153 could be a good candidate for a binary black hole. In the binary black hole scenario, the distance between the primary black hole and the secondary black hole is a ∼ 1.83 × 1016 cm.

In this work, we have searched for quasi-periodic oscillations (QPOs) in the 15 GHz light curve of the FSRQ PKS J0805--0111 monitored by the Owens Valley Radio Observatory (OVRO) 40 m telescope during the period from 2008 January 9 to 2019 May 9, using the weighted wavelet Z-transform (WWZ) and the Lomb-Scargle Periodogram (LSP) techniques. This is the first time to search for a periodic radio signal in the FSRQ PKS J0805–0111 by these two methods. Both methods consistently reveal a repeating signal with a periodicity of 3.38 ± 0.8 yr (>99.7% confidence level). In order to determine the significance of the periods, the false alarm probability method was applied, and a large number of Monte Carlo simulations were performed. As possible explanations, we discuss a number of scenarios including the thermal instability of thin disks scenario, the spiral jet scenario and the binary supermassive black hole scenario. We expect that the binary black hole scenario, where the QPO is caused by the precession of binary black holes, is the most likely explanation. FSRQ PKS J0805-0111 thus could be a good binary black hole candidate. In the binary black hole scenario, the distance between the primary black hole and the secondary black hole is about 1.71 × 1016 cm.

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