Accreting SMBH binaries: GRMHD simulations of the Gravitational Wave-driven regime

I will briefly review the status of theoretical modeling of magnetized circumbinary accretion disks when the SMBH binary is inspiraling and coalescing due to the emission of Gravitational Waves. I report results from simulations in General Relativity of magnetized disks accreting onto orbiting, inspiraling and merging black hole binaries, starting from relaxed disk initial data. The simulations feature an effective, rapid radiative
cooling scheme as a limiting case of future treatments with radiative transfer. I will show the importance of magnetic fields and potential implications of radiative cooling. An analysis of the dependence on the binary mass ratio is also discussed. The results are contrasted with simulations of the same initial disk around a single, non-spinning black hole. Apart from the resulting gravitational waveforms, estimates for various forms of possible outgoing radiation are discussed. The luminosity associated with local cooling is larger than the luminosity associated with matter kinetic outflows, while the electromagnetic (Poynting) luminosity associated with bulk transport of magnetic field energy is the smallest.
The presentation will include visualizations that highlight the presence of incipient jets throughout the evolution. Such jets are launched independently of the mass ratio, while the same initial disk accreting on a single non-spinning black hole does not lead to a jet, as expected. I will discuss a transient behavior in the collimated, magnetized outflows after merger: the outflows become increasingly magnetically dominated and accelerated to higher velocities, boosting the Poynting luminosity. I will discuss potential implications and prospects for a possible identification based on electromagnetic signatures and list our current, ongoing efforts to improve the models.