  Binary black holes emit gravitational waves as they inspiral towards
coalescence. Searches for electromagnetic counterparts to these gravitational
waves rely on looking for common sources producing both signals. In this paper,
we take a different approach: we investigate the impact of radiation zone
effects, including retardation effects and gravitational wave propagation onto
the circumbinary disk around stellar-mass, spinning black holes, using general
relativistic hydrodynamical simulations. Then we used a general relativistic
ray-tracing code to extract its X-ray spectrum and lightcurve. This allowed us
to show that radiation zone effects leave an imprint onto the disk, leading to
quasi-periodic patterns in the X-ray lightcurve. The amplitude of the
modulation is weak (<1%) but increases with time and is strongly dependent on
the inclination angle.
