Presentation #131.09 in the session Supernovae I.
Shock breakout (SBO), the first expected electromagnetic signature of a supernova (SN), can be an important probe of the progenitor of the explosion, but is difficult to capture due to its brief timescale. However, SBO may be extended when dense circumstellar material (CSM) is present. Indeed, recent photometric modeling studies of SNe, as well as early spectroscopy, suggest that such dense CSM may be present more often than previously expected. If true, this should also affect the features of SBO. Here I summarize the impact of such CSM interaction on the SBO width and luminosity, which I explore through both analytic and numerical modeling. As a specific example, SN PS1-13arp showed an early UV excess that has been argued to be SBO in dense CSM. Fitting this event with my models, I constrain the CSM parameters needed to understand PS1-13arp and conclude with a discussion of the implications for enhanced mass loss when massive stars are at the end of their lives.