Constrain the density slope of the secondary lens galaxy

Constrain the density slope of the secondary lens galaxy G2 in the SN 2025wny lens system beyond the adopted prior interval 1.6 <= eta_2 <= 2.4, using additional lensing or dynamical information.

Background

The authors fit models in which the density slopes of both lens galaxies are allowed to vary over the interval 1.6 <= eta_i <= 2.4. The primary lens G1 is consistent with an approximately isothermal profile, while G2 prefers a steeper profile with eta_2 approximately 2.3.

Because the posterior for G2 approaches the upper boundary of the adopted prior, the current imaging data do not determine that slope internally. This unresolved slope affects the inferred lens potential and contributes to the systematic uncertainty in the time-delay cosmographic estimate of H_0.

References

We note that the posterior distribution for the slope of the secondary lens galaxy approaches the upper boundary of the adopted prior, indicating that this parameter is not fully constrained by the present data.

— Follow-up of SN 2025wny V: Lens Modelling and Cosmography of a Strongly Lensed Superluminous Supernova at $z = 2.015$ using Space Data  (2608.28430 - Mörtsell et al., 28 Aug 2026) in Section 4.3, “Hubble constant constraints”