Study of a 43 day optical quasi-periodic oscillation for BL Lac S5 0716+714

TL;DR

This study detects a 43-day optical quasi-periodic oscillation in BL Lac S5 0716+714, revealing insights into jet dynamics and superimposed longer-term variability using advanced time-series analysis methods.

Contribution

First detection of a 43-day QPO in optical data of S5 0716+714 using Lomb-Scargle and wavelet methods, linking it to jet blob motion and precession.

Findings

Detected a 43-day QPO with >95% confidence

QPO explained by spiral motion of jet blob

Longer QPO superimposed on shorter oscillation

Abstract

The data for BL Lac object S5 0716+714 optical B, R and I bands are collected from November 10, 2017 to May 15, 2018. The raw data consists of 21396 quasi-simultaneous multi-band points, with 7132 data points for each band. To search for the quasi-periodic oscillation (QPO) signal of S5 0716+714, the Lomb Scargle periodogram (LSP) method and the Weighted Wavelet Z-transform (WWZ) method are used, and the light curve simulation method is utilized to estimate the significance level of the QPO. For the first time, a QPO with 43-day (> 95% confidence level) of approximate moon-like oscillations is revealed using these techniques. Furthermore, further research indicates that optical radiation is produced as a result of relativistic jet. This 43-day QPO can be explained by a spiral motion of a blob with velocity $\vec \beta$ along the jet. In addition, this 43-day QPO is superimposed on a longer QPO, and this superposition phenomenon can explain the linear upward trend. The viewing angle of the blob undergoes periodic changes, while jet precession results in a longer QPO. When the longer QPO fluxes are increasing state, a periodic rising tendency may be observed.