Paper detail

Testing cosmic opacity with the combination of strongly lensed and unlensed supernova Ia

In this paper, we present a scheme to investigate the opacity of the Universe in a cosmological-model-independent way, with the combination of current and future measurements of type Ia supernova sample and galactic-scale strong gravitational lensing systems with SNe Ia acting as background sources. The observational data include the current newly-compiled SNe Ia data (Pantheon sample) and simulated sample of SNe Ia observed by the forthcoming Large Synoptic Survey Telescope (LSST) survey, which are taken for luminosity distances ($D_L$) possibly affected by the cosmic opacity, as well as strongly lensed SNe Ia observed by the LSST, which are responsible for providing the observed time-delay distance ($D_{Δt}$) unaffected by the cosmic opacity. Two parameterizations, $τ(z)=2βz$ and $τ(z)=(1+z)^{2β}-1$ are adopted for the optical depth associated to the cosmic absorption. Focusing on only one specific type of standard cosmological probe, this provides an original method to measure cosmic opacity at high precision. Working on the simulated sample of strongly lensed SNe Ia observed by the LSST in 10 year $z$-band search, our results show that, with the combination of the current newly-compiled SNe Ia data (Pantheon sample), there is no significant deviation from the transparency of the Universe at the current observational data level. Moreover, strongly lensed SNe Ia in a 10 year LSST $z$-band search would produce more robust constraints on the validity of cosmic transparency (at the precision of $Δβ=10^{-2}$), with a larger sample of unlensed SNe Ia detected in future LSST survey. We have also discussed the ways in which our methodology could be improved, with the combination of current and future available data in gravitational wave (GW) and electromagnetic (EM) domain.