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Abstract

We present results from fully general relativistic (GR), three-dimensional
(3D), neutrino-radiation magneto-hydrodynamic (MHD) simulations of stellar core
collapse of a 20 M$_\odot$ star with spectral neutrino transport. Our focus is
to study the gravitational-wave (GW) signatures from the magnetorotationally
(MR)-driven models. By parametrically changing the initial angular velocity and
the strength of the magnetic fields in the core, we compute four models. Our
results show that the MHD outflows are produced only for models (two out of
four), to which rapid rotation and strong magnetic fields are initially
imposed. Seen from the direction perpendicular to the rotational axis, a
characteristic waveform is obtained exhibiting a monotonic time increase in the
wave amplitude. As previously identified, this stems from the propagating MHD
outflows along the axis. We show that the GW amplitude from anisotropic
neutrino emission becomes more than one order-of-magnitude bigger than that
from the matter contribution, whereas seen from the rotational axis, both of
the two components are in the same order-of-magnitudes. Due to the memory
effect, the frequency of the neutrino GW from our full-fledged 3D-MHD models is
in the range less than $\sim$10Hz. Toward the future GW detection for a
Galactic core-collapse supernova, if driven by the MR mechanism, the planned
next-generation detector as DECIGO is urgently needed to catch the
low-frequency signals.