2026ApJ...998..196L

We analyzed over four decades of UMRAO monitoring of PKS 1127-145 at 4.8, 8, and 14.5 GHz to search for quasiperiodic oscillations (QPOs) under red-noise variability. Lomb-Scargle and Weighted Wavelet Z-transform results from 10 day binned light curves were benchmarked against 10⁵ Monte Carlo red-noise realizations. We fit autoregressive moving-average (ARIMA) models to 30 day binned light curves to capture stochastic variability, and then assess periodic components by analyzing the periodograms of the model residuals. A ∼1000 day QPO (rest-frame ∼460 days) is locally significant in both the 8 and 14.5 GHz bands, with the strongest global support at 8 GHz; at 4.8 GHz we find evidence for a ∼3300 day component that is weaker and less reliable owing to the limited number of cycles. The confinement of the shorter period to higher frequencies points to a compact, upstream origin. Plausible mechanisms include orbital motion in a supermassive black hole binary, Lense-Thirring precession of a tilted inner flow, and the motion of a relativistic knot along a preexisting helical jet. In the helical case, VLBI kinematics constrain a Doppler factor δ ≈ 21, sufficient to compress an intrinsic ∼26 yr driver into the observed modulation, thereby connecting central-engine dynamics to the radio QPO.