The Variability Patterns of the TeV Blazar PG 1553+113 from a Decade of MAGIC and Multi-Band Observations

PG 1553+113 is one of the few blazars with a convincing quasi-periodicemission in the gamma-ray band. The source is also a very high-energy (VHE;>100 GeV) gamma-ray emitter. To better understand its properties and identifythe underlying physical processes driving its variability, the MAGICCollaboration initiated a multiyear, multiwavelength monitoring campaign in2015 involving the OVRO 40-m and Medicina radio telescopes, REM, KVA, and theMAGIC telescopes, Swift and Fermi satellites, and the WEBT network. Theanalysis presented in this paper uses data until 2017 and focuses on thecharacterization of the variability. The gamma-ray data show a (hint of a)periodic signal compatible with literature, but the X-ray and VHE gamma-raydata do not show statistical evidence for a periodic signal. In other bands,the data are compatible with the gamma-ray period, but with a relatively highp-value. The complex connection between the low and high-energy emission andthe non-monochromatic modulation and changes in flux suggests that a simpleone-zone model is unable to explain all the variability. Instead, a modelincluding a periodic component along with multiple emission zones is required.