We report on the gravitational wave signal computed in the context of a three-dimensional simulation of a core collapse supernova explosion of a 15 Solar mass star. The simulation was performed with our neutrino hydrodynamics code Chimera. We detail the gravitational wave strains as a function of time, for both polarizations, and discuss their physical origins. We also present the corresponding spectral signatures. Gravitational wave emission in our model has two key features: low-frequency emission (< 200 Hz) emanates from the gain layer as a result of neutrino-driven convection and the SASI and high-frequency emission (> 600 Hz) emanates from the proto-neutron star due to Ledoux convection within it. The high-frequency emission dominates the gravitational wave emission in our model and emanates largely from the convective layer itself, not from the convectively stable layer above it, due to convective overshoot. Moreover, the low-frequency emission emanates from the gain layer itself, not from the proto-neutron star, due to accretion onto it. We provide evidence of the SASI in our model and demonstrate that the peak of our low-frequency gravitational wave emission spectrum corresponds to it. Given its origin in the gain layer, we classify the SASI emission in our model as p-mode emission and assign a purely acoustic origin, not a vortical-acoustic origin, to it. Our dominant proto-neutron star gravitational wave emission is not well characterized by emission from surface g-modes, complicating the relationship between peak frequencies observed and the mass and radius of the proto-neutron star expressed by analytic estimates under the assumption of surface g-mode emission. We present our frequency normalized characteristic strain along with the sensitivity curves of current- and next-generation gravitational wave detectors.
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