Binary Black-Hole Mergers in Magnetized Disks: Simulations in Full
  General Relativity
  We present results from the first fully general relativistic,
magnetohydrodynamic (GRMHD) simulations of an equal-mass black hole binary
(BHBH) in a magnetized, circumbinary accretion disk. We simulate both the pre
and post-decoupling phases of a BHBH-disk system and both "cooling" and
"no-cooling" gas flows. Prior to decoupling, the competition between the binary
tidal torques and the effective viscous torques due to MHD turbulence depletes
the disk interior to the binary orbit. However, it also induces a two-stream
accretion flow and mildly relativistic polar outflows from the BHs. Following
decoupling, but before gas fills the low-density "hollow" surrounding the
remnant, the accretion rate is reduced, while there is a prompt electromagnetic
(EM) luminosity enhancement following merger due to shock heating and accretion
onto the spinning BH remnant. This investigation, though preliminary, previews
more detailed GRMHD simulations we plan to perform in anticipation of future,
simultaneous detections of gravitational and EM radiation from a merging
BHBH-disk system.
