A Gravitationally Lensed Quasar at the Epoch of Reionization

A high fraction of the most luminous high-redshift quasars was predicted to be lensed due to magnification bias. We report the discovery of a strongly lensed ultraluminous quasar at z = 6.51, the first such object detected at the epoch of reionization and the brightest quasar yet known at z > 5. High-resolution HST imaging reveals a multiple imaged system with a maximum image separation 0.2", best explained by a model of three quasar images lensed by a low luminosity galaxy at z~0.7, with a magnification factor of ~50. This discovery suggests that a significant population of strongly lensed, high redshift quasars could have been missed by previous surveys, as standard color selection fails when the quasar color is contaminated by the lensing galaxy flux.