Serendipitous discovery of quadruply-imaged quasars: two diamonds
  Gravitationally lensed quasars are powerful and versatile astrophysical
tools, but they are challengingly rare. In particular, only ~25
well-characterized quadruple systems are known to date. To refine the target
catalogue for the forthcoming Taipan Galaxy Survey, the images of a large
number of sources are being visually inspected in order to identify objects
that are confused by a foreground star or galaxies that have a distinct
multi-component structure. An unexpected by-product of this work has been the
serendipitous discovery of about a dozen galaxies that appear to be lensing
quasars, i.e. pairs or quartets of foreground stellar objects in close
proximity to the target source. Here we report two diamond-shaped systems.
Follow-up spectroscopy with the IMACS instrument on the 6.5m Magellan Baade
telescope confirms one of these as a z = 1.975 quasar quadruply lensed by a
double galaxy at z = 0.293. Photometry from publicly available survey images
supports the conclusion that the other system is a highly sheared
quadruply-imaged quasar. In starting with objects thought to be galaxies, our
lens finding technique complements the conventional approach of first
identifying sources with quasar-like colours and subsequently finding evidence
of lensing.
