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 ($D_{\Delta t}$) unaffected by the cosmic opacity.
Two parameterizations, $\tau(z)=2\beta z$ and $\tau(z)=(1+z)^{2\beta}-1$ 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 $\Delta\beta=10^{-2}$), 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.
