Presentation #111.16 in the session “Time Domain Astrophysics (Poster)”.
Core-collapse supernovae can display evidence of interaction with pre-existing, circumstellar shells of material by rebrightening and forming spectral lines, and can even change types as Hydrogen appears in previously Hydrogen-poor spectra. However, a recently observed core-collapse supernova — SN 2019tsf — was found to brighten after roughly 100 days after it was first observed, suggesting that the supernova ejecta was interacting with surrounding material, but it lacked any observable emission lines and thereby challenged the standard supernova-interaction picture. We show through linear perturbation theory that delayed rebrightenings without the formation of spectral lines are generated as a consequence of the finite sound crossing time of the post-shock gas left in the wake of a supernova explosion. In particular, we demonstrate that sound waves — generated in the post-shock flow as a consequence of the interaction between a shock and a density enhancement — traverse the shocked ejecta and impinge upon the shock from behind in a finite time, generating sudden changes in the shock properties in the absence of ambient density enhancements. This model therefore provides a mechanism for generating supernovae that brighten at late times but lack the emission lines that are characteristic of circumstellar interaction.