  We model the electromagnetic emission signatures of massive black hole
binaries (MBHBs) with an associated gas component. The method comprises
numerical simulations of relativistic binaries and gas coupled with
calculations of the physical properties of the emitting gas. We calculate the
accretion powered UV/X-ray and Halpha light curves and the Halpha emission line
profiles. The simulations have been carried out with a modified version of the
parallel tree SPH code Gadget. The heating, cooling, and radiative processes
for the solar metallicity gas have been calculated with the photoionization
code Cloudy. We investigate gravitationally bound, sub-parsec binaries which
have not yet entered the gravitational radiation phase. The results from the
first set of calculations, carried out for a coplanar binary and gas disk,
suggest that the outbursts in the X-ray light curve are pronounced during
pericentric passages and can serve as a fingerprint for this type of binaries
if periodic outbursts are a long lived signature of the binary. The Halpha
emission-line profiles also offer strong indications of a binary presence and
may be used as a criterion for selection of MBHB candidates for further
monitoring from existing archival data. The orbital period and mass ratio of a
binary could be determined from the Halpha light curves and profiles of
carefully monitored candidates. Although systems with the orbital periods
studied here are not within the frequency band of the Laser Interferometer
Space Antenna (LISA), their discovery is important for understanding of the
merger rates of MBHBs and the evolution of such binaries through the last
parsec and towards the detectable gravitational wave window.
