Accretion disks around binary black holes of unequal mass: GRMHD
  simulations of postdecoupling and merger
  We report results from simulations in general relativity of magnetized disks
accreting onto 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. Here we evolve the
systems after binary-disk decoupling through inspiral and merger, and analyze
the dependence on the binary mass ratio with $q\equiv m_{\rm bh}/M_{\rm
BH}=1,1/2,$ and $1/4$. We find that 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 cooling luminosity around merger
is only marginally smaller than that of a single, non-spinning black hole.
Incipient 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. For all mass ratios we see a transient behavior in the
collimated, magnetized outflows lasting $2-5 ( M/10^8M_\odot ) \rm days$ after
merger: the outflows become increasingly magnetically dominated and accelerated
to higher velocities, boosting the Poynting luminosity. These sudden changes
can alter the electromagnetic emission across the jet and potentially help
distinguish mergers of black holes in AGNs from single accreting black holes
based on jet morphology alone.
