Breaking the Mass-sheet Degeneracy in Time-delay Cosmology with Lensed and Unlensed Type Ia Supernovae

Abstract

This study introduces an innovative framework aimed at overcoming the ongoing issue of mass-sheet degeneracy (MSD) in time-delay cosmography by incorporating observations of both gravitationally lensed and unlensed Type Ia supernovae (SNe Ia). By simultaneously using lensing magnification measurements $μ^{\rm{obs}}$ and cosmic distance ratios ($D_s/D_{ds}$), we develop a Bayesian framework capable of breaking the MSD. Specifically, we reconstruct the distance-redshift and magnitude-redshift relations from unlensed Type Ia supernovae using Gaussian process to avoid dependence on specific cosmological models. Our framework shows substantial efficacy in resolving the MSD by imposing constraints on the MSD parameter $λ$. Furthermore, we extend this framework to analyze multiple gravitational lensing systems. The results show strong agreement with the fiducial MSD parameters used in the data simulation, confirming our method's effectiveness in mitigating the MSD. Ultimately, this technique enables the derivation of corrected time-delay distance measurements under the MSD, improving the precision of cosmological parameters inferred from strong lensing systems.

Figures (14)

• Figure 1: The time-delay distance ($D_{\Delta t}$) and angular-diameter distance to the lens ($D_{\rm{d}}$), along with the magnification ratios of the lensed images. The results are derived from a power-law lens model in Lenstronomy, with the incorporation of an intrinsic MSD parameter.
• Figure 2: The simulated observation of magnitudes $m^{\rm{obs}}_{\rm{unlensed}}$ and the reconstructed magnitudes $m^{\rm{GP}}_{\rm{unlensed}}$ .
• Figure 3: The reconstructed unanchored luminosity distance $(D_LH_0)^{\rm{GP}}_{\rm{unlensed}}$ from simulated distance module based on flat $\rm{\Lambda}CDM$ model.
• Figure 4: Simulated lensed magnitudes $m^{\rm{obs}}_{\rm{lensed}}(z_s)$ with a total error of 0.28 mag.
• Figure 5: Simulated observational magnifications for lensed Type Ia supernovae at $z_{\rm{s}} = 1.5$, $z_{\rm{d}}=0.5$.