| Abstract: | We examine the photospheric time evolution of two recent and well-observed core-collapse supernovae (CCSNe), SN 2023ixf and SN 2024ggi, and identify distinct evolutionary phases characterized by nearly constant expansion velocities - two in SN 2024ggi and two (or possibly three) in SN 2023ixf. We interpret these phases as evidence for the presence of two (or three) distinct nested ejecta shells. To explore this interpretation, we construct a simple toy model for CCSN ejecta consisting of two shells: an outer, low-mass spherical shell and an inner, massive, elongated shell. We show that this model successfully reproduces the observed evolution of the photospheric radius, Rph(t), of SN 2024ggi. The non-spherical ejecta geometry is motivated by the observed morphologies of several CCSN remnants. Previous studies of our group have associated such remnant morphologies with the jittering-jet explosion mechanism (JJEM), in which two or three energetic pairs of jets contribute to driving the explosion. We therefore conclude that the inferred photospheric shell structure in SN 2023ixf and SN 2024ggi supports an explosion powered by the JJEM. |