Discovery of a strongly lensed galaxy at z=3.9 behind a z=0.83 galaxy cluster

We report on the discovery and spectroscopic confirmation of three gravitational ly-lensed images of a galaxy at z = 3.9 in the background of a distant, rich cluster of galaxies at z = 0.83, on the basis of observations with Faint Object Camera And Spectrograph on the Subaru telescope. We construct a simple lens model of the cluster mass distribution based on Jee et al.'s weak lensing mass estimates from deep, high-resolution images by Advanced Camera for Surveys on the Hubble Space Telescope. The lens model can account simultaneously for the observed image configuration and the flux ratio of the closer pair located close to the critical curve. The parities of the three images are also consistent with the lensing hypothesis. Since this galaxy is apparently bright (i'(AB) similar to 23.7) for its redshift due to magnification, it serves as a good high-redshift target on which we can make extensive and detailed studies based on multi-wavelength imaging and spectroscopy.