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tokens: observed data. However, it is worth noting that the end frequency may be difficult to detect as LIGO is not currently very sensitive to frequencies above ∼1000 Hz. Figure 11. Example of GW quantities considered in the correlation matrix for a 15 M ⊙ progenitor with α Λ = 1.25, which does not explode successfully. The blue line is the early slope between 500 and 1000 Hz, and the orange line shows the slope just prior to collapse , between collapse to a BH and 500 Hz below the final frequency. These quantities will be used to compare between simulations and explore correlations with properties of the progenitor and explosion. Green line is the function fit of the peak GW frequency after 0.5 s postbounce. Although the parameters we consider seem rudimentary, we experimented with using various arbitrary functional fits to the frequency evolution with time, but found that as with the neutrino evolution, the fitting parameters were not well correlated with the progenitor and explosion process, especially in comparison with the parameters we have adopted. For example, Morozova et al. ( 2018 ) used a quadratic fit of the form to characterize the peak GW frequency between 0.5 and 1.5 s postbounce. However, we have found that although this functional fit captures well the shape of the peak frequency at early times, it fails to capture the behavior as the peak frequency levels out at late times ( t > 1.5 s postbounce). We propose instead a fit of the form , which better captures the behavior at later times. An example of such a fit is shown in Figure 11 . The coefficients of both functional fits are not well correlated with properties of the progenitor or explosion. Nonetheless, such fits may be useful for studies of detectability, as priors in LIGO data searches, etc., and thus the fit coefficients can be found online, 11 11 Publicly available at [doi: 10.5281/zenodo.3822555 ]. but we will not discuss them further in this work in our exploration of correlated quantities. It is easiest to see how these GW parameters change with the properties of the progenitor and explosion by looking at the correlation matrix. Figure 12 shows the correlation matrix between progenitor, explosion, and GW properties for simulations that explode successfully. Again, there are many additional parameters that could be included, but all showed weak correlations with the GW emission and thus we do not include them here. The GW eigenfrequencies are intimately related to the PNS mass and the core compactness ξ 2.5 , because they are sensitive to the structure of the core and its evolution. Figure 12. Correlation matrix for observable GW quantities and underlying progenitor and explosion properties for simulations that successfully explode. The quantities considered are core compactness ( ξ 2.5 ), PNS mass () at 1 s postbounce, explosion energy ( E expl ), and early peak GW frequency slope () between 500 and 1000 Hz. The lower-left half shows the correlation strength, ranging