J1721+8842: a gravitationally lensed binary quasar with a proximate damped Lyman-

High-redshift binary quasars provide key insights into mergers and quasar activity, and are useful tools for probing the spatial kinematics and chemistry of galaxies along the line of sight. However, only three sub-10-kpc binaries have been confirmed above z = 1. Gravitational lensing would provide a way to easily resolve such binaries, study them in higher resolution, and provide more sightlines, though the required alignment with a massive foreground galaxy is rare. Through image deconvolution of StanCam Nordic Optical Telescope (NOT) monitoring data, we reveal two further point sources in the known, z ≈ 2.38, quadruply lensed quasar (quad) J1721+8842. An ALFOSC/NOT long-slit spectrum shows that the brighter of these two sources is a quasar with z = 2.369 ± 0.007 based on the C III