The Hubble Constant from SN Refsdal

Hubble Space Telescope observations from 2015 December 11 detected the expected fifth counter-image of supernova (SN) Refsdal at z = 1.49. In this Letter, we compare the time-delay predictions from numerous models with the measured value derived by Kelly et al. from very early data in the light curve of the SN Refsdal and find a best value for (68% CL), in excellent agreement with predictions from cosmic microwave background and recent weak lensing data + baryon acoustic oscillations + Big Bang nucleosynthesis (from the DES Collaboration). This is the first constraint on H ₀ derived from time delays between multiple-lensed SN images, and the first with a galaxy cluster lens, subject to systematic effects different from other time-delay H ₀ estimates. Additional time-delay measurements from new multiply imaged SNe will allow derivation of competitive constraints on H ₀.