GRMHD Simulations of Accretion Flows Onto Massive Binary Black Hole Mergers Embedded in a Thin Slab of Gas

We present general relativistic magnetohydrodynamic simulations of mergingequal-mass, spinning black holes embedded in an equatorial thin slab ofmagnetized gas. We evolve black holes either non-spinning, with spins alignedto the orbital angular momentum, and with misaligned spins. The rest-massdensity of the gas slab follows a Gaussian profile symmetric relative to theequatorial plane and it is initially either stationary or with Keplerianrotational support. As part of our diagnostics, we follow the accretion ofmatter onto the black hole horizons and the Poynting luminosity. Throughout theinspiral phase, the configurations with non-zero spins display modulations inthe mass accretion rate that are proportional to the orbital frequency and itsmultiples. Our frequency analysis suggests that these modulations areinfluenced by the initial geometry and angular momentum of the gasdistribution. In contrast to binary models evolved in the gas cloud scenario,we do not observe a significant increase in the mass accretion rate after themerger in any of our simulations. This observation brings attention to apotential link between the electromagnetic signatures of massive binary blackhole mergers and the geometrical distribution of the surrounding gas. It alsosuggests the possibility of not detecting a peak luminosity at the time ofmerger in future electromagnetic observations.