Determining cosmological-model-independent H0 and post-Newtonian parameter with time-delay lenses and supernovae

Abstract

ABSTRACT Strong gravitational lensing provides a natural opportunity to test general relativity (GR). We propose a model-independent method for simultaneous constraining on Hubble constant (H0) and post-Newtonian parameter (γPPN) using strong lensing systems and observational Type Ia supernovae. The time-delay measurements from strong lensing can directly determine the Hubble constant, and the lens distance inferred from the spectroscopic measurement of the stellar kinematics of the deflector galaxy can help us to constrain the post-Newtonian parameter. We seek the Pantheon data set and reconstruct unanchored distances using Gaussian process regression to achieve the cosmological-model-independent GR testing instead of assuming a specific model, which can reduce possible bias on GR testing and measurement of Hubble constant. Combining the reconstructed unanchored distances and the four H0LiCOW lens data sets, our results are $H_0=72.9^{+2.0}_{-2.3} \, \mathrm{km \, s^{-1} \, Mpc^{-1}}$ and $\gamma _{\rm {PPN}}=0.89^{+0.17}_{-0.15}$. All the lenses show that there is no obvious evidence to support GR deviation within observational uncertainties. In the subsequent analysis, we consider a ratio of distance ${D_{\Delta t}}/{D^{^{\prime }}_{\mathrm{ d}}}$ method to further avoid the influence of H0 on GR testing. The results show that, except J1206 within the ∼1.2σ observational uncertainty, the remaining three lenses support that GR holds within the 1σ observational uncertainties.