  Supermassive black hole binaries (SMBHBs) are natural by-products of galaxy
mergers and are expected to be powerful multi-messenger sources. They can be
powered by the accretion of matter and then radiate across the electromagnetic
spectrum, much like normal active galactic nuclei (AGNs). Current
electromagnetic observatories have a good chance of detecting and identifying
these systems in the near future. However, precise observational indicators are
needed to distinguish individual AGNs from SMBHBs. In this paper, we propose a
novel electromagnetic signature from SMBHBs: non-thermal emission produced by
the interaction between the jets ejected by the black holes. We study close
SMBHBs, which accrete matter from a circumbinary disc and the mini-discs formed
around each hole. Each black hole ejects a magnetically dominated jet in the
direction of its spin through the Blandford--Znajeck mechanism. We argue that
in such a situation, the interaction between the jets can trigger strong
magnetic reconnection events, where particles are accelerated and emit
non-thermal radiation. Depending on whether the jets are aligned or misaligned,
this radiation can have different periodicities. We model the evolution of the
particles accelerated during the dual jet interaction and calculate their
radiative output, obtaining spectra and providing estimates for the variability
timescales. We finally discuss how this emission compares with that of normal
AGNs.
