Müller et al.  have modeled the emission of GWs from anisotropic neutrino emission from convection both inside and above the proto neutron star for non-rotating models. The signal from the proto neutron star is shown in Figure 26. Note that although the quadrupole amplitude for the neutrino emission is much higher, it varies slower than the mass motions. Hence, it only dominates the signal at low frequencies. This model is of a cooling, isolated proto neutron star that developed much stronger convection than is seen in proto neutron star models of full systems. As such, it represents an upper limit for the GW signal of non-rotating proto neutron stars. Figure 26 shows the signal for the convection above the proto neutron star. Like in the case of neutrino emission for proto neutron star convection, anisotropic neutrino emission from convection above the proto neutron star dominates the low-frequency part of the signal.
For mass motions, rotation strongly increases the signal at bounce and during the convective phase. But the neutrino signal does not increase as dramatically. Kotake et al.  found that the signal from a rotating collapse is dominated at nearly all frequencies by the matter contribution (Figure 27). This is because the neutrino signal is axially symmetric and the variation in the quadrupole moment is fairly weak. However, within the SASI paradigm, Kotake et al.  found that the amplitude of the GW signal is two orders of magnitude larger than those from convective matter motions outside the proto neutron star. This result has been confirmed by several groups [195, 228].
The asymmetric collapse simulations discussed in Section 4.2 are one way to increase the GW signal from anisotropic neutrino emission. Recall from Figure 17 that Burrows & Hayes found that the neutrino-induced term dominated the GW signal for their asymmetric collapse simulations. Fryer et al.  found the same result. The GW amplitude is dominated by the neutrino component and can exceed , for a source located at 10 Mpc in Fryer’s most extreme example. A caveat in this result is that Fryer et al. were artificially increasing the level of the asymmetry in the collapse in an attempt to obtain strong neutron star kicks and it is unlikely that any stellar system will have such large asymmetries in nature. This signal estimate should be seen as an extreme upper limit.
Anisotropic neutrino emission has several distinguishing features that will allow us to differentiate it from a matter-driven GW signal. It has much less variation in the time structure and will produce a stronger signal at lower frequencies. But much more work must be done to understand fully the neutrino-driven GW signal. For example, GWs can be produced by asymmetric neutrino emission from the core (e.g., from oscillations with sterile neutrinos ). If magnetic fields induce asymmetries in this oscillation and the neutron star is rotating, the sterile neutrino emission can produce a neutrino-driven GW signature that is very different from what was shown here.
Living Rev. Relativity 14, (2011), 1
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