Lunch talk on Oct. 12, 2026

Systematics in Strong-lensing Time-delay Modeling

Speaker:  Guanhua Rui (Shanghai Normal University)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Monday, Oct. 12, 2026

Abstract: 

Strong-lensing time delays provide an independent route to measuring the Hubble constant. As both the sample size and observational precision improve, systematics are becoming increasingly important in time-delay cosmography. They enter at different stages of the analysis, from time-delay measurements based on variable-source light curves, to mass-model assumptions and possible mass-model mismatch, the mass-sheet degeneracy, line-of-sight effects, and the final cosmological inference. In this talk, I will present our studies of several major systematics in lensed quasars and lensed Type Ia supernovae. For lensed SNe Ia, I will discuss the effects of microlensing, photometric uncertainties, and observing cadence on time-delay measurements. For lensed quasars, I will focus on mass-profile assumptions, mass-model mismatch, and the mass-sheet degeneracy, using WGD 2038−4008 as an example. I will also briefly discuss other effects such as external convergence, source reconstruction, and PSF modeling.