  We study the evolution of accretion disk around a supermassive binary black
hole with equal mass using non-relativistic hydrodynamical simulations
performed with FARGO3D. Compared with previous studies with the Newtonian
hydrodynamics, here, we adopt the post-Newtonian hydrodynamics using the near
zone metric of the binary black hole. In contrast to the Newtonian
investigation, we find that there is a dramatic difference in the
post-Newtonian regime, gap formed by the circumbinary accretion disk around the
binary with equal mass is wider with the post-Newtonian hydrodynamics than that
with the Newtonian hydrodynamics and is independent of disk viscosity given
that hydrodynamical simulations are run for about the same factor times the
viscous timescale associated with different viscosities. This may present
unique observable signatures of the continuum emission in such binary-disk
system.
