Abstract :
The blazar 3C 66A is known for its optical flux periodicity and complex jet kinematics. Using 22/43 GHz KaVa (KVN and VERA array) observations and 43 GHz VLBA (Very Long Baseline Array) archival data, we have found that its pc-scale jet has a twisted structure and that the inner jet undergoes periodic swings every 11 years. In this talk, we will describe the peculiar characteristics of 3C 66A and delve into possible interpretation scenarios. The multiwavelength flux variability and jet orientation changes hint at a supermassive black hole binary (SMBHB) in which orbital motion and disk-orbit misalignment lead to jet precession. However, combinations of other mechanisms such as Lense-Thirring disk precession and jet instabilities could also account for the properties of 3C 66A, underscoring the challenge in robust SMBHB candidate identification. We will briefly discuss the growing number of SMBHB candidates that are being reported with different methods and the need for a catalogue allowing future analyses to discriminate among them.
