Possible quasi-periodic optical oscillations of ZTF blazars

TL;DR

This study analyzes optical light curves of 10 ZTF blazars, identifying potential quasi-periodic oscillations in four sources and suggesting nonlinear variability processes, with some signals reaching near-significant statistical levels.

Contribution

It presents the first detailed analysis of QPOs in ZTF blazars using multiple detection methods, highlighting candidate periodicities and variability characteristics.

Findings

Four blazars show candidate QPOs with periods of 38.5 to 630 days.

Optical variability exhibits a linear RMS-Flux relation and log-normal flux distribution.

Two blazars have signals with global significance around 2.5-2.7 sigma.

Abstract

Based on the Zwicky Transient Facility (ZTF), we selected 10 blazars as our sample sources. Among these, we found four blazars (J 0923.5+4125, J 1221.3+3010, J 1503.5+4759, and J 1652.7+4024) showing possible indications of quasi periodic oscillations (QPOs) modulation. We conducted a detailed analysis of their optical light curves (g- and r-bands) over the past five years using the root mean square (RMS)-Flux relation, flux distribution, and QPO detection methods to investigate their variability characteristics. A linear RMS-Flux relation is present in both bands, and their flux distributions follow a log-normal form. This suggests that optical variability may arise from multiplicative, nonlinear processes across different timescales and flux states. Further QPO analysis using the weighted wavelet Z-transform (WWZ), Lomb-Scargle periodogram (LSP), and autoregressive integrated moving average (ARIMA) methods identified candidate periodic signals in four blazars. J 0923.5+4125 (period $\sim$ 205 days) and J 1221.3+3010 ($\sim$ 630 days) show local significances of $\sim 3 \sigma$, whereas J 1503.5+4759 ($\sim$ 38.5 days) and J 1652.7+4024 ($\sim$ 48 days) reach $\sim 4 \sigma$. After accounting for the look-elsewhere effect, the global significances for J 1503.5+4759 in the g- and r-bands are $\sim 2.7 \sigma$, while for J 1652.7+4024 they are approximately $\sim 2.5 \sigma$ in both bands. These two blazars warrant further monitoring and investigation.