BayeSN-TD: Time Delay and H 0 Estimation for Lensed SN H0pe

Abstract

We present BayeSN-TD, an enhanced implementation of the probabilistic Type Ia supernova (SN Ia) BayeSN spectral energy distribution (SED) model, designed for fitting multiply-imaged gravitationally lensed Type Ia supernovae (glSNe Ia). BayeSN-TD fits for magnifications and time delays across multiple images while marginalizing over an achromatic Gaussian process-based treatment of microlensing, to allow for time-dependent deviations from a typical SN Ia SED caused by gravitational lensing by stars in the lensing system. BayeSN-TD is able to robustly infer time delays and produce well-calibrated uncertainties, even when applied to simulations based on a different SED model and incorporating chromatic microlensing, strongly validating its suitability for time-delay cosmography. We then apply BayeSN-TD to publicly available photometry of the glSN Ia SN H0pe, inferring time delays between images BA and BC of d and d along with absolute magnifications for each image, , , and . Combining our constraints on time delays and magnifications with existing lens models of this system, we infer km s Mpc, consistent with previous analysis of this system; incorporating additional constraints based on spectroscopy yields km s Mpc. While this is not yet precise enough to draw a meaningful conclusion with regard to the ‘Hubble tension’, upcoming analysis of SN H0pe with more accurate photometry enabled by template images, and other glSNe, will provide stronger constraints on ; BayeSN-TD will be a valuable tool for these analyses.