Speaker
Description
The oscillation modes of neutron star (NS) merger remnants, as encoded by the kHz post-merger gravitational wave (GW) signal, hold great potential for constraining the as-yet undetermined equation of state (EOS) of dense nuclear matter. Previous works have used numerical relativity simulations to derive quasi-universal relations for the key oscillation frequencies, but most of them omit the effects of a magnetic field. We conduct fully general-relativistic, magnetohydrodynamics simulations of NSNS mergers with two different masses, two different EOSs (SLy and ALF2), three different magnetic field topologies just prior to merger (pure poloidal and pure toroidal, both confined to the interior, and "pulsar-like" poloidal extending from the interior to the exterior), and with four different initial magnetic field strengths. We find that magnetic braking and magnetic turbulent viscosity drive the merger remnants towards uniform rotation and increase the overall angular momentum loss. This loss causes the remnant to contract, resulting in a time-dependent increase in the fundamental quadrupole f2 GW frequency. The overall shift is up to ~ 200 Hz for the strongest magnetic field considered and ≲ 50 Hz for the median case. This shift will be degenerate with competing effects coming from the equation of state, mass ratios, and prior spins. Isolating an f2 ≲ 100 Hz shift from any individual effect will be challenging for current or future GW observations, which should include the magnetic field in their analyses.
