Multi-messenger signatures of supermassive black hole binaries

Supermassive black hole binaries (SMBHBs) are the natural end-product of galaxy mergers and should be common in galactic nuclei. At the final stage of their evolution, binaries can be identified from their bright electromagnetic emission, as quasars with periodic variability, and from their strong gravitational radiation (e.g., by Pulsar Timing Arrays-PTAs). I will discuss synergies between electromagnetic and gravitational wave signatures of SMBHBs, connecting both signals to the orbital dynamics of the binary. I will show that currently multi-messenger detections are possible only for the most massive and nearby galaxies, limited by the sensitivity of PTAs, but in the next 5-10yr joint observations will become feasible for a wider variety of binaries.