Signatures of supermassive black hole binaries on maser systems
  We illustrate a novel signature of black hole binaries from their effect on
the kinematics of water maser emission in their environments. With the help of
simulations, we establish the condition for clumps to mase based on their
coherence lengths calibrated to those of the known maser galaxy NGC 4258. This
is then used to identify masing clumps around a binary black hole system, and
quantify the kinematic and spectral differences relative to the single black
hole case. For some generic circumstances, blue-shifted masers around a binary
black hole are found to preferentially follow the Keplerian rotation curve
observed in the single black hole case. The redshifted ones, however, are found
to visibly deviate from this relation, and also display more scatter with a
tendency towards lower absolute values of the velocity along the line-of-sight.
The spectrum of the masers as a function of line-of-sight velocity also shows a
double peaked structure, reminiscent of recent observations of systems such as
Mrk 1. Our results motivate future prospects for identifying binary black hole
candidates with the help of water maser emissions.
