James Webb Space Telescope Feed Post

Arxiv: SN H0pe: The First Measurement of H_0 from a Multiply-Imaged Type Ia Supernova, Discovered by JWST Published: 3/27/2024 8:00:08 PM Updated: 12/2/2024 8:35:34 PM

Paper abstract: The first James Webb Space Telescope ({\it JWST}) Near InfraRed Camera(NIRCam) imaging in the field of the galaxy cluster PLCK G165.7+67.0 (z=0.35)uncovered a Type Ia supernova (SN Ia) at z=1.78, called ``SN H0pe." Threedifferent images of this one SN were detected as a result of stronggravitational lensing, each one traversing a different path in spacetime,thereby inducing a relative delay in the arrival of each image. Follow-up {\itJWST} observations of all three SN images enabled photometric and rarespectroscopic measurements of the two relative time delays. Following strictblinding protocols which oversaw a live unblinding and regulatedpost-unblinding changes, these two measured time delays were compared to thepredictions of seven independently constructed cluster lens models to measure avalue for the Hubble constant, H_0=71.8^{+9.2}_{-8.1} km s^{-1} Mpc^{-1}.The range of admissible H_0 values predicted across the lens models limitsfurther precision, reflecting the well-known degeneracies between lens modelconstraints and time delays. It has long been theorized that a way forward isto leverage a standard candle, but this has not been realized until now. Forthe first time, the lens models are evaluated by their agreement with the SNabsolute magnifications, breaking degeneracies and producing our best estimate,H_0=75.7^{+8.1}_{-5.5} km s^{-1} Mpc^{-1}. This is the first precisionmeasurement of H_0 from a multiply-imaged SN Ia and only the second from anymultiply-imaged SN.