PG 1553+113 is a distant TeV blazar known for its ~2.2-year periodic gamma-ray signal detected with Fermi-LAT. We present results from a decade-long, multiwavelength monitoring campaign of this source. Our analysis confirms the periodicity in gamma-ray and optical bands; however, no significant periodicity is found at TeV and X-ray energies, based on observations with MAGIC and Swift-XRT, respectively. These findings, combined with a study of variability on different timescales, support a multi-zone emission scenario, as further corroborated by recent IXPE observations. We test a two-zone, synchrotron self-Compton model on 2019 multi-frequency flare data. The long- and short-term variability, along with inter-band correlations from the monitoring, serve as key inputs to constrain the model, reducing the large degrees of freedom. Based on this approach, we propose a set of parameters that effectively describe the PG 1553+113 emitting region responsible for the observed radiation.
Prandini et al. (Wed,) studied this question.