Cosmological constraints from the double source plane lens SDSSJ0946+1006

We present constraints on the equation of state of dark energy, w, and the total matter density, Omega(M), derived from the double-source-plane strong lens SDSSJ0946+1006, the first cosmological measurement with a galaxy-scale double-source-plane lens. By modelling the primary lens with an elliptical power-law mass distribution, and including perturbative lensing by the first source, we are able to constrain the cosmological scaling factor in this system to be beta(-1) = 1.404 +/- 0.016, which implies Omega(M) = 0.33(-0.26)(+0.33) for a flat Lambda cold dark matter (Lambda CDM) cosmology. Combining with a cosmic microwave background prior from Planck, we find omega = -1.17(-0.21)(+0.20) assuming a flat omega CDM cosmology. This inference shifts the posterior by 1 sigma and improves the precision by 30 per cent with respect to Planck alone, and demonstrates the utility of combining simple, galaxy-scale multiple-source-plane lenses with other cosmological probes to improve precision and test for residual systematic biases.