Convection signatures in early-time gravitational waves from core-collapse supernovae

Context. Gravitational wave emitted from core collapse supernova explosions are critical observables for extracting information about the dynamics and properties of both the progenitor and the post-bounce evolution of the system. They are prime targets for current interferometric searches and represent a key milestone for the capabilities of next-generation interferometers. Aims. This study aims to characterise how the gravitational waveform associated with prompt stellar convection depends on the rotational rate and magnetic field topology of the progenitor star. Methods. We carried out a series of axisymmetric simulations of a 16.5 M⊙ red supergiant with five configurations of initial magnetic fields and varying degrees of initial rotation. We analysed the contribution of early-time convection and the proto-neutron star core to the waveform using ensemble empirical mode decomposition, alongside spectral and Fourier analyses, to facilitate the comparison and interpretation of the results. Results. Our simulations show that the first six intrinsic mode functions dominate the early post-bounce gravitational wave signal, with variations due to rotation and magnetic fields influencing the signal strength. Strong magnetic fields decelerate core rotation, affecting mode excitation. Regardless of the initial rotation, convection consistently drives a low-frequency mode that lasts throughout the evolution. Conclusions. We conclude that prompt convection can produce gravitational wave amplitudes comparable to or exceeding those of core bounce, with a persistent low-frequency component detectable in next-generation detectors.