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3.3 GW emission mechanisms

Gravitational radiation will be emitted during the collapse/explosion of a core collapse SN due to the star’s changing quadrupole moment. A rough description of the possible evolution of the quadrupole moment is given in the remainder of this paragraph. During the first 100 -250 ms of the collapse, as the core contracts and flattens, the magnitude of the quadrupole moment I- ij will increase. The contraction speeds up over the next 20 ms and the density distribution becomes a centrally condensed torus [170Jump To The Next Citation Point]. In this phase the core’s shrinking size dominates its increasing deformation and the magnitude of I-ij decreases. As the core bounces, I-ij changes rapidly due to the deceleration and rebound. If the bounce occurs because of nuclear pressure, its timescale will be < 1 ms. If centrifugal forces play a role in halting the collapse, the bounce can last up to several ms [170Jump To The Next Citation Point]. The magnitude of I-ij will increase due to the core’s expansion after bounce. As the resulting shock moves outwards, the unshocked portion of the core will undergo oscillations, causing I-ij to oscillate as well. The shape of the core, the depth of the bounce, the bounce timescale, and the rotational energy of the core all strongly affect the GW emission. For further details see [71170Jump To The Next Citation Point].

Convectively driven inhomogeneities in the density distribution of the outer regions of the nascent neutron star and anisotropic neutrino emission are other sources of GW emission during the collapse/explosion (see [41Jump To The Next Citation Point176Jump To The Next Citation Point80Jump To The Next Citation Point158] for reviews).

As discussed in the case of AIC, global rotational instabilities (such as the m = 2 bar-mode) may develop during the collapse itself or in a neutron star remnant. A neutron star remnant will likely also be susceptible to the radiation reaction driven r-modes. Both of these types of instabilities will emit GWs, as will a fragmentation instability if one occurs. See Section 2.3 for further details regarding these instabilities.


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