Strongly lensed candidates from the HSC transient survey
  We present a lensed quasar search based on the variability of lens systems in
the HSC transient survey. Starting from 101,353 variable objects with i-band
photometry in the HSC transient survey, we used a variability-based lens search
method measuring the spatial extent in difference images to select potential
lensed quasar candidates. We adopted conservative constraints in this
variability selection and obtained 83,657 variable objects as possible lens
candidates. We then ran CHITAH, a lens search algorithm based on the image
configuration, on those 83,657 variable objects, and 2,130 variable objects
were identified as potential lensed objects. We visually inspected the 2,130
variable objects, and seven of them are our final lensed quasar candidates.
Additionally, we found one lensed galaxy candidate as a serendipitous
discovery. Among the eight final lensed candidates, one is the only known
quadruply lensed quasar in the survey field, HSCJ095921+020638. None of the
other seven lensed candidates have been previously classified as a lens nor a
lensed candidate. Three of the five final candidates with available HST images,
including HSCJ095921+020638, show clues of a lensed feature in the HST images.
A tightening of variability selection criteria might result in the loss of
possible lensed quasar candidates, especially the lensed quasars with faint
brightness or narrow separation, without efficiently eliminating the non-lensed
objects; CHITAH is therefore important as an advanced examination to improve
the lens search efficiency through the object configuration. The recovery of
HSCJ095921+020638 proves the effectiveness of the variability-based lens search
method, and this lens search method can be used in other cadenced imaging
surveys, such as the upcoming Rubin Observatory Legacy Survey of Space and
Time.
