A New Kilohertz Gravitational-wave Feature from Rapidly Rotating Core-collapse Supernovae

Abstract

We present self-consistent three-dimensional core-collapse supernova simulations of a rotating 20 M _⊙ progenitor model with various initial angular velocities from 0.0 to 4.0 rad s ^−1 using the smoothed particle hydrodynamics code SPHYNX and the grid-based hydrodynamics code FLASH . We identify two strong gravitational-wave features with peak frequencies of ∼300 Hz and ∼1.3 kHz in the first 100 ms postbounce. We demonstrate that these two features are associated with the m = 1 deformation from the proto-neutron star (PNS) modulation induced by the low- T /∣ W ∣ instability, regardless of the simulation code. The 300 Hz feature is present in models with an initial angular velocity between 1.0 and 4.0 rad s ^−1 , while the 1.3 kHz feature is only present in a narrower range, from 1.5 to 3.5 rad s ^−1 . We show that the 1.3 kHz signal originates from the high-density inner core of the PNS, and the m = 1 deformation triggers a strong asymmetric distribution of electron antineutrinos. In addition to the 300 Hz and 1.3 kHz features, we also observe one weaker but noticeable gravitational-wave feature from higher-order modes in the range between 1.5 and 3.5 rad s ^−1 . Its initial peak frequency is around 800 Hz, and it gradually increases to 900–1000 Hz. Therefore, in addition to the gravitational bounce signal, the detection of the 300 Hz, 1.3 kHz, the higher-order mode, and even the related asymmetric emission of neutrinos could provide additional diagnostics for estimating the initial angular velocity of a collapsing core.

Keywords

• Core-collapse supernovae
• Gravitational wave astronomy
• Hydrodynamical simulations
• Neutron stars