Indication for Dual Periodic Signatures in PKS 0805-07 from Multi-technique Time Series Analysis

TL;DR

This study identifies two significant quasi-periodic oscillations in the gamma-ray light curve of PKS 0805-07, suggesting complex jet variability possibly driven by geometric effects like jet precession rather than a binary black hole system.

Contribution

First detection of dual QPOs in a blazar's gamma-ray emission using multiple time-series analysis techniques, supporting a geometric origin of variability.

Findings

Two statistically significant QPOs at ~255 and 112 days.

Dual oscillatory components have comparable amplitudes, out of phase.

Variability likely caused by jet precession and interference effects.

Abstract

We report the identification of two statistically significant quasi-periodic oscillations in the weekly binned $\gamma$-ray light curve of the flat-spectrum radio quasar PKS 0805$-$07, observed by Fermi-LAT over the period MJD 59047.5-59740.5. By applying a suite of complementary time-series analysis techniques, we identify periodic signatures at approximately 255 and 112 days. These techniques include the Lomb-Scargle periodogram (LSP), Weighted Wavelet Z-transform (WWZ), REDFIT, Date-Compensated Discrete Fourier Transform (DCDFT), Phase Dispersion Minimization (PDM), and the String-length method. The reliability of these signals is supported by high local significance (> 99) in all methods and reinforced through phase-folding. Model selection using the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) strongly supports a two-component periodic model. The detection of dual QPOs is rare among blazars and suggests complex variability mechanisms. Although a binary supermassive black hole (SMBH) scenario could be considered given the sources high redshift (z = 1.837), the short periodicities are difficult to reconcile with orbital motion unless invoking extreme parameters. Double-sine model fitting reveals that the oscillatory components have comparable amplitudes but are out of phase, suggesting a potential beating phenomenon due to interference. This amplitude-modulated variability is consistent with a geometric origin, most plausibly jet precession driven by Lense-Thirring torques, superimposed with a secondary process such as polar jet oscillation. Doppler factor modulation arising from these effects can account for the observed flux variations without requiring an unrealistically compact binary.