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Abstract

The construction of accurate and consistent initial data for various binary
parameters is a critical ingredient for numerical relativity simulations of the
compact binary coalescence. In this article, we present an upgrade of the
pseudospectral SGRID code, which enables us to access even larger regions of
the binary neutron star parameter space. As a proof of principle, we present a
selected set of first simulations based on initial configurations computed with
the new code version. In particular, we simulate two millisecond pulsars close
to their breakup spin, highly compact neutron stars with masses at about $98\%$
of the maximum supported mass of the employed equation of state, and an unequal
mass systems with mass ratios even outside the range predicted by population
synthesis models ($q = 2.03$). The discussed code extension will help us to
simulate previously unexplored binary configurations. This is a necessary step
to construct and test new gravitational wave approximants and to interpret
upcoming binary neutron star merger observations. When we construct initial
data, one has to specify various parameters, such as a rotation parameter for
each star. Some of these parameters do not have direct physical meaning, which
makes comparisons with other methods or models difficult. To facilitate this,
we introduce simple estimates for the initial spin, momentum, mass, and center
of mass of each individual star.