Detection of a high-confidence quasi-periodic oscillation in radio light curve of the high redshift FSRQ PKS J0805-0111

TL;DR

This study reports the detection of a significant quasi-periodic oscillation with a 3.38-year period in the radio light curve of the high-redshift FSRQ PKS J0805-0111, suggesting a possible binary black hole system.

Contribution

First combined use of WWZ and LSP methods to identify a QPO in the radio light curve of PKS J0805-0111, proposing a binary black hole scenario as the most likely explanation.

Findings

Detected a 3.38-year QPO with >99.7% confidence

Supported binary black hole precession as the likely cause

Estimated black hole separation of about 1.71×10^{16} cm

Abstract

In this work, we have searched 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 January 9,2008 to May 9,2019, using the weighted wavelet Z-transform (WWZ) and the Lomb-Scargle Periodogram (LSP) techniques. This is the first time to search for periodic radio signal in the FSRQ PKS J0805-0111 by these two methods. All two methods consistently reveal a repeating signal with a periodicity of 3.38$\pm$ 0.8 years ($>$99.7\% confidence level). In order to determining the significance of the periods, the false alarm probability method was used, 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 expected that the binary black hole scenario, where the QPO is caused by the precession of the 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 $1.71\times 10^{16}$ cm.