  We present general relativistic magneto-hydrodynamical simulations of
equal-mass spinning black hole binary mergers embedded in a magnetized gas
cloud. We focus on the effect of the spin orientation relative to the orbital
angular momentum on the flow dynamics, mass accretion rate and Poynting
luminosity. We find that, across the inspiral, the gas accreting onto the
individual black holes concentrates into disk-like overdensities, whose angular
momenta are oriented towards the spin axes and which persist until merger. We
identify quasi-periodic modulations occurring in the mass accretion rate at the
level of 1-20%, evolving in parallel with the gravitational wave chirp. The
similarity between the accretion rate time-series and the gravitational strain
is a consequence of the interplay between strong, dynamical gravitational
fields and magnetic fields in the vicinity of the inspiralling black holes.
This result suggests that quasi-periodicity in the pre-merger accretion rate of
massive binaries is not exclusive of environments in which the black holes are
embedded in a circumbinary accretion disk, and could provide an additional
useful signature of electromagnetic emission concurrent to low-frequency
gravitational wave detection.
