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 merging equal-mass spinning black holes embedded in an equatorial thin slab of magnetized gas. We explore configurations with black holes that are nonspinning, with spins aligned to the orbital angular momentum, and with misaligned spins. The rest-mass density of the gas slab follows a Gaussian profile symmetric relative to the equatorial plane and it is initially either stationary or with Keplerian rotational support. As part of our diagnostics, we track the accretion of matter onto the black hole horizons and the Poynting luminosity. Throughout the inspiral phase, configurations with nonzero spins display modulations in the mass accretion rate that are proportional to the orbital frequency and its multiples. Frequency analysis suggests that these modulations are a generic feature of inflows on merging binaries. In contrast to binary models evolved in a gas cloud scenario, we do not observe a significant increase in the mass accretion rate after the merger in any of our simulations, suggesting the possibility of not detecting a peak luminosity at the time of merger in future electromagnetic observations.