Gravitationally Lensed Quasars in Gaia: II. Discovery of 24 Lensed
  Quasars
  We report the discovery, spectroscopic confirmation and preliminary
characterisation of 24 gravitationally lensed quasars identified using Gaia
observations. Candidates were selected in the Pan-STARRS footprint with
quasar-like WISE colours or as photometric quasars from SDSS, requiring either
multiple detections in Gaia or a single Gaia detection near a morphological
galaxy. The Pan-STARRS grizY images were modelled for the most promising
candidates and 60 candidate systems were followed up with the William Herschel
Telescope. 13 of the lenses were discovered as Gaia multiples and 10 as single
Gaia detections near galaxies. We also discover 1 lens identified through a
quasar emission line in an SDSS galaxy spectrum. The lenses have median image
separation 2.13 arcsec and the source redshifts range from 1.06 to 3.36. 4
systems are quadruply-imaged and 20 are doubly-imaged. Deep CFHT data reveal an
Einstein ring in one double system. We also report 12 quasar pairs, 10 of which
have components at the same redshift and require further follow-up to rule out
the lensing hypothesis. We compare the properties of these lenses and other
known lenses recovered by our search method to a complete sample of simulated
lenses to show the lenses we are missing are mainly those with small
separations and higher source redshifts. The initial Gaia data release only
catalogues all images of ~ 30% of known bright lensed quasars, however the
improved completeness of Gaia data release 2 will help find all bright lensed
quasars on the sky.
