The Unexpected, Long-Lasting, UV Rebrightening of the Super-Luminous Supernova ASASSN-15lh

Understand

Given its peak luminosity and early-time spectra, ASASSN-15lh was classified as the most luminous supernova (SN) ever discovered (Dong et al.

• 2016).
• Here we report a UV rebrightening of ASASSN-15lh observed with Swift during our follow-up campaign.
• The rebrightening began at $t \simeq$ 90 days (observer frame) after the primary peak and was followed by a $\sim 120$-day long plateau in the bolometric luminosity, before starting to fade again at $t\simeq 210$ days.