Gravitational waves or x-ray counterpart? No need to choose

Binary black holes emit gravitational waves (GWs) as they inspiral toward coales-cence. Searches for electromagnetic counterparts to these GWs rely on looking for common sources producing both signals. In this article, 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.