Model-independent Estimations for the Cosmic Curvature from the Latest Strong Gravitational Lensing Systems

Model-independent measurements for the cosmic spatial curvature, which is related to the nature of cosmic space-time geometry, plays an important role in cosmology. On the basis of the Distance Sum Rule in the Friedmann-Lema{\^i}tre-Robertson-Walker metric, (distance ratio) measurements of strong gravitational lensing (SGL) systems together with distances from type Ia supernovae observations have been proposed to directly estimate the spatial curvature without any assumptions for the theories of gravity and contents of the universe. However, previous studies indicated that a spatially closed universe was strongly preferred. In this paper, we re-estimate the cosmic curvature with the latest SGL data which includes 163 well-measured systems. In addition, possible factors, e.g. combination of SGL data from different surveys and stellar mass of the lens galaxy, which might affect estimations for the spatial curvature, are considered in our analysis. We find that, except the case where only SGL systems from the Sloan Lens ACS Survey are considered, a spatially flat universe is consistently favored at very high confidence level by the latest observations. It is suggested that the increasing number of well-measured strong lensing events might significantly reduce the bias of estimation for the cosmic curvature.