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We perform simulations of general relativistic rotating stellar core collapseand compute the gravitational waves (GWs) emitted in the core bounce phase ofthree representative models via multiple techniques. The simplest technique,the quadrupole formula (QF), estimates the GW content in the spacetime from themass quadrupole tensor. It is strictly valid only in the weak-field andslow-motion approximation. For the first time, we apply GW extraction methodsin core collapse that are fully curvature-based and valid for stronglyradiating and highly relativistic sources. We employ three extraction methodscomputing (i) the Newman-Penrose (NP) scalar Psi_4, (ii)Regge-Wheeler-Zerilli-Moncrief (RWZM) master functions, and (iii)Cauchy-Characteristic Extraction (CCE) allowing for the extraction of GWs atfuture null infinity, where the spacetime is asymptotically flat and the GWcontent is unambiguously defined. The latter technique is the only one notsuffering from residual gauge and finite-radius effects. All curvature-basedmethods suffer from strong non-linear drifts. We employ the fixed-frequencyintegration technique as a high-pass waveform filter. Using the CCE results asa benchmark, we find that finite-radius NP extraction yields results that agreenearly perfectly in phase, but differ in amplitude by ~1-7% at core bounce,depending on the model. RWZM waveforms, while in general agreeing in phase,contain spurious high-frequency noise of comparable amplitudes to those of therelatively weak GWs emitted in core collapse. We also find remarkably goodagreement of the waveforms obtained from the QF with those obtained from CCE.They agree very well in phase but systematically underpredict peak amplitudesby ~5-11% which is comparable to the NP results and is within the uncertaintiesassociated with core collapse physics. (abridged)

Gravitational Wave Extraction in Simulations of Rotating Stellar Core Collapse