Speaker : Ragnhild Lunnan
Title: A Circumstellar Shell around a Superluminous Supernova Revealed in a Light Echo
Abstract: Superluminous supernovae (SLSNe) are a rare class of transients with peak luminosities 10-100 times those of normal core-collapse and Type Ia SNe, and whose progenitors and energy sources are still debated. Here, I will report on a surprising result from our Keck late-time spectroscopic survey of SLSNe: the discovery of a shell of circumstellar material (CSM) around the supernova, revealed by both absorption and subsequent re-emission in Mg II from the shell, in an “echo” of the SN light. The blueshift of the absorption lines allow us to measure the velocity of the CSM shell, while the time delay between the blueshifted and redshifted emission lines directly constrains the size of the shell. While pre-supernova mass loss is not uncommon in massive stars, this kind of observation is nearly unique, with the closest observed analogue being the ionization of the ring around SN1987A by the supernova flash. I will discuss both the circumstances that allowed us to observe it in this particular instance, and the implications for superluminous supernova progenitors and mass loss mechanisms. In this case, the high shell velocity (~3000 km/s) and implied time of the eruption (~40 years prior to explosion) may point to a pulsational pair-instability origin.
