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Abstract

Detectable electromagnetic counterparts to gravitational waves from compact
binary mergers can be produced by outflows from the black hole-accretion disk
remnant during the first ten seconds after the merger. Two-dimensional
axisymmetric simulations with effective viscosity remain an efficient and
informative way to model this late-time post-merger evolution. In addition to
the inherent approximations of axisymmetry and modeling turbulent angular
momentum transport by a viscosity, previous simulations often make other
simplifications related to the treatment of the equation of state and turbulent
transport effects.
In this paper, we test the effect of these modeling choices. By evolving with
the same viscosity the exact post-merger initial configuration previously
evolved in Newtonian viscous hydrodynamics, we find that the Newtonian
treatment provides a good estimate of the disk ejecta mass but underestimates
the outflow velocity. We find that the inclusion of heavy nuclei causes a
notable increase in ejecta mass. An approximate inclusion of r-process effects
has a comparatively smaller effect, except for its designed effect on the
composition. Diffusion of composition and entropy, modeling turbulent transport
effects, has the overall effect of reducing ejecta mass and giving it a speed
with lower average and more tightly-peaked distribution. Also, we find
significant acceleration of outflow even at distances beyond 10,000\,km, so
that thermal wind velocities only asymptote beyond this radius and at somewhat
higher values than previously reported.