Initial Configuration
We consider an SMS model just prior to collapse, when it is described by a uniformly rotating $\Gamma=4/3$ polytrope spinning at the mass-shedding limit. The SMS is of arbitrary mass M and has an angular momentum $J/M^2=0.96$ and a rotational-to-gravitational-binding-energy ratio $\mathcal{T}/|W|=0.009$. The equatorial radius of the star is $R_{\rm eq}=626M\approx 9.25\times 10^6\,({M}/{10^6M_{\odot}})$ km; the polar radius satisfies $R_p/R_{eq}=2/3$. This model is marginally unstable to radial instability due to GR, which triggers the collapse. The SMS is seeded with a dipole-like magnetic field which extends from to stellar interior into the exterior. We choose the magnetic field strength so that the ratio of magnetic to the rotational kinetic energy is $\mathcal{M}/\mathcal{T} = 0.1$. The average magnetic field strength is given by $\langle B \rangle = 6.5\times{10^6}({10^6\,M_\odot}/{M})\rm\,G$.
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