Extended material at large radii surrounding a supernova can result in a double-peaked light curve .
This occurs when the material is sufficiently massive that the supernova shock continues to propagate into it and sufficiently extended that it produces a bright first peak .
Such material can be the leftover , low-mass envelope of a star that has been highly stripped , the mass associated with a wind , or perhaps mass surrounding the progenitor due to some type of pre-explosion activity .
I summarize the conditions necessary for such a light curve to occur , describe what can be learned about the extended material from the light curve shape , and provide an analytic model for fitting the first peak in these double-peaked supernovae .
This is applied to the specific case of a Type Ic super-luminous supernova , LSQ14bdq .
The mass in the extended material around this explosion ’ s progenitor is measured to be small , \sim 0.3 - 0.5 M _ { \odot } .
The radius of this material can be \sim 500 - 5 @ 000 R _ { \odot } , but it is difficult to constrain due to a degeneracy between radius and the supernova ’ s energy .
In the future , spectra taken during the first peak will be important for measuring the velocity and composition of the extended material so that this degeneracy can be overcome .