Multiwavelength quasi-periodic variability of the blazar Ton 599

ABSTRACT During the last 40–50 yr, the TeV blazar Ton 599 has systematically experienced major outbursts detected in a wide wavelength range from radio to $\gamma$-rays. In this work, we present an analysis of Ton 599 quasi-periodic variability across multiple wavelengths using an observing baseline from 1983 to 2025. The $\gamma$-ray, optical, and radio emissions are found to be highly correlated with time lags $\sim 0$–360 d, which indicates that they are triggered by the same population of particles. Using the Lomb–Scargle periodogram and the Weighted Wavelet Z-transform, we revealed several periodic components with characteristic periods of 1.4, 1.7, 2.3, 6.5, and 7.5 yr. The result is consistent with the detection of periodic components in the 1997–2011 light curves, which means that we observe the same mechanism causing long-term periodic variability. A model of a binary supermassive black hole (SMBH) with a precessing jet, applied to the radio light curves of Ton 599, yields frequency-dependent best-fitting parameters with orbital periods ranging from $\sim$1.2 to 1.7 yr and precession periods from $\sim$5.8 to 7.7 yr. This result implies the existence of an SMBH system modulating emission through both the orbiting and jet precession effects, with differing observed periods possibly reflecting frequency-dependent emission regions along a structured stratified jet. None the less, the short-term periodicity and exceptionally strong flares likely arise from internal jet shocks, which aligns with typical blazar behaviour. We suggest that the multiband quasi-periodicity of Ton 599 is reasonably described by a combination of geometric effects (orbital motion and precession) and stochastic processes.