Misaligned snowplough effect and the electromagnetic counterpart to
  black hole binary mergers
  We estimate the accretion rates produced when a circumprimary gas disc is
pushed into the primary supermassive black hole (SMBH) by the tidal force of
the decaying secondary during a SMBH merger. Using the 3D Smoothed Particle
Hydrodynamics (SPH) code {\sc phantom}, we extend previous investigations of
co-planar discs to the case where the disc and binary orbital planes are
misaligned. We consider a geometrically thin disc with inclination angles
varying from 1 to 180 degrees and a binary with mass ratio $q$=$10^{-3}$. We
find that discs with small inclination angles (< 10 degrees) produce an
increase in luminosity exceeding the Eddington rate. By contrast, discs with
inclinations between 20 and 30 degrees show a less pronounced rise in the
accretion rate, whilst discs inclined by 180 degrees show no peak in the mass
accretion rate. While previous analytic work predicted that the effective tidal
torque drops with increasing inclination angle, we show that the misaligned
snowplough effect remains important even for angles larger than the disc aspect
ratio. The rise in the accretion rate produced by discs inclined at small
angles to the binary orbit can produce an electromagnetic counterpart to the
gravitational wave signal emitted from final stages of the binary orbital
decay.
