Joel Johansson: Discovering and dissecting lensed supernovae

Thursday 17 Sept 2026, 13:15 → 14:00 Europe/Stockholm

A5:1003 (AlbaNova Main Building)

Strong gravitational lensing provides nature’s own telescopes, magnifying distant supernovae and allowing us to study stellar explosions at redshifts that would otherwise be difficult to reach. When a supernova is multiply imaged, the different light paths also introduce time delays between the images, providing an independent route to measuring the expansion rate of the Universe.
In this talk, I will present the discovery and analysis of two recent strongly lensed supernovae: SN 2025mkn, a Type II supernova at z=1.37, and SN 2025wny, the first strongly lensed Type I superluminous supernova (SLSN-I), at z=2.0. I will discuss how gravitational magnification, combined with extensive imaging and spectroscopy, allows us to dissect these distant explosions and follow their evolution in unusual detail.
I will focus on a new approach to measuring lensing time delays using the temporal evolution of supernova spectra. For SN 2025wny, tracking the spectral evolution of its multiple images yields some of the most precise time-delay measurements obtained for a lensed supernova to date, including a ~5% measurement of its longest delay. Together with detailed modelling of the lens system, these spectroscopic time delays provide a new route to measuring the Hubble constant and demonstrate the potential of future samples of lensed supernovae for precision cosmology.