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 we show using one-dimensional radiation-hydrodynamic SN
models 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,
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 that 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.Comment: 9 pages, 7 figures, submitted for publication in The Astrophysical
Journa