  We present the results of 2D, moving mesh, viscous hydrodynamical simulations
of accretion onto merging supermassive black hole (SMBH) binaries. We include
viscous heating, shock heating, and radiative cooling, and simulate the
transition from the "pre-decoupling" epoch, where the inspiral timescale is
longer than the viscous timescale, to the "post-decoupling" epoch, where the
inspiral timescale is shorter than the viscous timescale. We find that there is
no abrupt halt to the accretion at decoupling, but rather the accretion shows a
slow decay, with significant accretion well after the expected decoupling.
Moreover, we find that the luminosity in X-rays is significantly higher prior
to the merger, as orbital energy from the SMBH binary is converted to heat via
strong shocks inside the cavity, and radiated away. Following the merger, the
cavity refills viscously and the accretion rate relaxes to the Shakura-Sunyaev
value, while the X-ray luminosity drops as the shocks quickly dissipate.
