2025/09/15 by Justin Pierel, Pierel, J. D. R., Erin E. Hayes +55
Physics and Astronomy · #Astronomy and Astrophysical Research #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2509.12301
openalex publication_date 2025/09/15 · openalex created_date 2025/10/18 · openalex updated_date 2026/07/28
Multiply-imaged supernovae (SNe) provide a novel means of constraining the Hubble constant (H0). Such measurements require a combination of precise models of the lensing mass distribution and an accurate estimate of the relative time delays between arrival of the multiple images. Only two multiply-imaged SNe, Refsdal and H0pe, have enabled measurements of H0 thus far. Here we detail the third such measurement for SN Encore, a z=1.95 SNIa discovered in JWST/NIRCam imaging. We measure the time delay, perform simulations of additional microlensing and millilensing systematics, and combine with the mass models of Suyu et al. in a double-blind analysis to obtain our H0 constraint. Our final time-delay measurement is Δt1b,1a=-39.8-3.3+3.9 days, which is combined with seven lens models weighted by the likelihood of the observed multiple image positions for a result of H0=66.9-8.1+11.2 \rmkm \rms-1\rmMpc-1. The uncertainty on this measurement could be improved significantly if template imaging is obtained. Remarkably, a sibling to SN Encore (SN "Requiem") was discovered in the same host galaxy, making the MACS J0138.0-2155 cluster the first system known to produce more than one observed multiply-imaged SN. SN Requiem has a fourth image that is expected to appear within a few years, providing an unprecedented decade-long baseline for time-delay cosmography and an opportunity for a high-precision joint estimate of H0.