The case for space: estimating precise time delays from ground- and space-based observations of lensed supernovae with Glimpse

The delay in arrival time of the multiple images of gravitationally lensed supernovae (glSNe) can be related to the present-day expansion rate of the universe, H₀. Despite their rarity, Rubin Observatory's Legacy Survey of Space and Time (Rubin-LSST) is expected to discover tens of galaxy-scale glSNe per year, many of which will not be resolved due to their compact nature. Follow-up from ground- and space-based telescopes will be necessary to estimate time delays to sufficient precision for meaningful H₀ constraints. We present the GLIMPSE model (GAUSSN Light curve Inference of Magnifications and Phase Shifts, Extended) that estimates time delays with resolved and unresolved observations together for the first time, while simultaneously accounting for dust and microlensing effects. With this method, we explore best follow-up strategies for glSNe observed by Rubin-LSST. For unresolved systems on the dimmest end of detectability by Rubin-LSST, having peak i-band magnitudes of 22─24 mag, the time delays are measured to as low as 0.7 d uncertainty with 6─8 epochs of resolved space-based observations in each of 4─6 optical and NIR (near-infrared) filters. For systems of similar brightness that are resolved by ground-based facilities, time delays are consistently constrained to 0.5─0.8 d precision with six epochs in four optical and NIR filters of space-based observations or eight epochs in four optical filters of deep ground-based observations. This work improves on previous time-delay estimation methods and demonstrates that glSNe time delays of ∼10−20 d can be measured to sufficient precision for competitive H₀ estimates in the Rubin-LSST era.