Program: GN-2016B-FT-21

All-sky transient surveys have revealed a new diversity in supernovae (SNe), including extreme events that are orders of magnitude brighter than other SNe. Some of these 'superluminous supernovae' (SLSNe) show hydrogen emission lines at a few thousand km/s, indicating that the ejecta are running into a massive circumstellar medium (CSM) and strongly interacting. Recently, our group has discovered and monitored one of the most luminous SNe yet detected, PS16aqy. This event evolved from a featureless spectrum to show very strong Balmer lines. However, at z=0.265, covering the broad Halpha profile in its entirety is difficult, and furthermore PS16aqy has now been fading for around 200 days. Using the large aperture afforded by Gemini and the red-sensitivity of GMOS, we can follow the shock interaction out to very late times from explosion to map out the CSM density profile, and ultimately constrain the progenitor mass and mass-loss mechanism for one of the most extreme interacting supernova-CSM systems known.