2017ApJ...838...28M

A longstanding problem in the study of supernovae (SNe) has been the relationship between the Type IIP and Type IIL subclasses. Whether they come from distinct progenitors or they are from similar stars with some property that smoothly transitions from one class to another has been the subject of much debate. Here, using one-dimensional radiation-hydrodynamic SN models, we show that the multi-band light curves of SNe IIL are well fit by ordinary red supergiants surrounded by dense circumstellar material (CSM). The inferred extent of this material, coupled with a typical wind velocity of ∼10–100 km s^–1, suggests enhanced activity by these stars during the last ∼months to ∼years of their lives, which may be connected with advanced stages of nuclear burning. Furthermore, we find that, even for more plateau-like SNe, dense CSM provides a better fit to the first ∼20  days of their light curves, indicating that the presence of such material may be more widespread than previously appreciated. Here we choose to model the CSM with a wind-like density profile, but it is unclear whether this just generally represents some other mass distribution, such as a recent mass ejection, thick disk, or even inflated envelope material. Better understanding the exact geometry and density distribution of this material will be an important question for future studies.