SDSS J1640+1932: a spectacular galaxy–quasar strong lens system.

We present Canada–France–Hawaii Telescope (CFHT) MegaCam observations of a galaxy–quasar strong gravitational lens system, SDSS J1640+1932. This system, located at z = 0.195 (foreground elliptical galaxy) and z = 0.778 (background quasar), was first visually identified by us in the Sloan Digital Sky Survey data base. Our CFHT imaging with an angular resolution of 0.7 arcsec clearly resolves four lensed images and a nearly complete Einstein ring. Modelling the system with a singular isothermal ellipsoid total mass distribution, we find an Einstein radius of 2.49''+0.063-0.049 enclosing an inferred mass of 7.25+0.37-0.29 × 1011 M⊙. The quasar and its host galaxy have been magnified by a factor of 23, and the time delay relative to the leading image is determined to be 23.4-25.2 d. These parameters vary minimally when our model is fitted to the g-, r- or i-band images. [ABSTRACT FROM AUTHOR]