GECO Transient circle : Cosmology and stellar physics with strongly lensed supernovaeCosmology and stellar physics with strongly lensed supernovae

For our next Transient Circle, we have the pleasure of having our own Raoul Canameras talking about supernovae gravitationally lensed, focusing on his recent groundbreaking work on the first superluminous supernova discovered to be strongly lensed.

Strongly lensed supernovae (SNe) enable independent measurements of the Hubble constant (H₀) through time-delay cosmography, offering a critical test of the current H₀ tension. Their rapid follow-up also enables unique diagnostics of early explosion physics and progenitor properties. In this talk, I will present forecasts for (a) measurements of the Hubble constant and (b) constraints on SN progenitors achievable with forthcoming samples of strongly lensed SNe from Rubin-LSST. I will then describe newly developed deep-learning approaches to search for lensed SNe in LSST with minimal contamination rates. I will also discuss the ongoing analysis and modeling of SN 2025wny (SN Winny) at zₛ = 2.008, the first confirmed galaxy-scale strongly lensed superluminous SN detected with ZTF in mid-2025. Spectroscopic follow-up of SN Winny reveals a blue continuum and weak UV features consistent with a hot Type I SLSN. Moreover, its long-time delays make SN Winny well-suited for independent measurements of the Hubble constant. I will present the follow-up campaign, characterization, and modeling of this exciting system and show how it paves the way for future analyses of larger samples selected by Rubin-LSST.