We perform general relativistic magnetohydrodynamic simulations of binary neutron star (BNS) mergers with four distinct magnetic field topologies: (i) a dipole pulsarlike configuration, (ii) a mixed linear superposition of poloidal and toroidal components inside the star, and (iii–iv) two topologies featuring a smooth transition from a confined mixed core to a pulsarlike structure at radii $0.95R_{\mathrm{NS}}$ and $0.5R_{\mathrm{NS}}$, with $R_{\mathrm{NS}}$ the radius of the star. The latter topologies are explored in BNS merger studies for the first time. We evolve systems with two equations of state, Skyrme-Lyon (SLy) and WFF1, with Arnowitt-Deser-Misner masses 2.7 and 2.6, respectively, and include an additional lower-mass SLy binary to probe the behavior of long-lived remnants. We perform an extensive analysis of the emission properties of the systems, both electromagnetic and gravitational waves, and of the properties of the remnants, namely their frequency modes, density eigenfunctions, rotation, temperature, and convective stability. We report three key results: (1) for the first time, we assess the convective stability of magnetized remnants, extending previous unmagnetized analyses; (2) we identify a clear secondary peak in the gravitational-wave spectrum of pulsarlike configurations, consistent with the nonlinear coupling of the $m=0$ and $m=2$ modes, which is absent in other topologies; and (3) the magnetic field topology strongly influences the gravitational wave emission properties to the extent that nearby ($<50\mathrm{Mpc}$) events could allow one to observationally distinguish between different field structures with future gravitational-wave detectors. Across all models, we obtain luminosities compatible with short $\gamma$-ray bursts, with purely poloidal configurations being the most efficient in driving possible relativistic jets.

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• Gravitational wave sources
• Gravitational waves
• Numerical simulations in gravitation & astrophysics