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Pulsar timing arrays (PTAs) may eventually be able to detect not only thestochastic gravitational-wave (GW) background of SMBH binaries, but alsoindividual, particularly massive binaries whose signals stick out above thebackground. In this contribution, we discuss the possibility of identifying andstudying such `resolved' binaries through their electromagnetic emission. Thehost galaxies of such binaries are themselves expected to be also very massiveand rare, so that out to redshifts z~2 a unique massive galaxy may beidentified as the host. At higher redshifts, the PTA error boxes are larger andmay contain as many as several hundred massive-galaxy interlopers. In thiscase, the true counterpart may be identified, if it is accreting gasefficiently, as an active galactic nucleus (AGN) with a peculiar spectrum andvariable emission features. Specifically, the binary's tidal torques expel thegas from the inner part of the accretion disk, making it unusually dim in X-rayand UV bands and in broad optical emission lines. The tails of the broad wingsof any FeK-alpha emission line may also be `clipped' and missing. The binary'sorbital motion, as well as the gas motions it induces, may triggerquasiperiodic variations. These include coherent flux variability, such asluminous, multi-wavelength flares, as well as Doppler shifts of broad emissionlines and `see-saw' oscillations in the FeK-alpha line. Additional features,such as evidence for a recent major merger or dual collimated jets, could alsocorroborate the counterpart. These properties would make resolved PTA sourcesstand out among AGN with similar overall luminosities and allow theiridentification.

Electromagnetic signatures of supermassive black hole binaries resolved by PTAs