Initial Configuration

The binaries consist of two identical, uniformly rotating NSs modeled with a $\Gamma=2$ polytropic EOS with spin $\chi_{\text{NS}}\equiv J_{\text{ql}}/(m)^2=0.36=a/m$, where $J_{\text{ql}}$ is the quasilocal angular momentum of the NS and $m=M/2$ where $M$ is the Arnowitt-Deser-Misner (ADM) mass of the system. The ADM mass of the system is $M=4.43(M_{NS}/1.625M_\odot)\rm km$, and has an initial coordinate binary separation of $45\,(M_{NS}/1.625 M_\odot)\rm km$.

To mimic the force-free magnetosphere surrounding the NS, and to reliably evolve the magnetic field outside the star, we set a variable exterior, low-density magnetosphere such as that $P_{\text{mag}}/ P_{\text{gas}}$ is $100$ everywhere. This density increases the total rest-mass of the system by $\lesssim 0.5\%$. For the subsequent evolution, we integrate the ideal GRMHD equations everywhere, imposing a density floor in regions where $\rho_0^{\text{atm}}\leq 10^{-10} \rho_0^{\text{max}}$, as is typically done in standard hydrodynamics schemes. Here $\rho_0^{\text{max}}$ is the initial maximum rest-mass density of the system.