Identifying lensed quasars and measuring their time-delays from
  unresolved light curves
  Identifying multiply imaged quasars is challenging due to their low density
in the sky and the limited angular resolution of wide field surveys. We show
that multiply imaged quasars can be identified using unresolved light curves,
without assuming a light curve template or any prior information. After
describing our method, we show using simulations that it can attain high
precision and recall when we consider high-quality data with negligible noise
well below the variability of the light curves. As the noise level increases to
that of the Zwicky Transient Facility (ZTF) telescope, we find that precision
can remain close to $100\%$ while recall drops to $\sim 60\%$. We also consider
some examples from the Time Delay Challenge 1 (TDC1) and demonstrate that the
time delays can be accurately recovered from the joint light curve data in
realistic observational scenarios. We further demonstrate our method by
applying it to publicly available COSMOGRAIL data of the observed lensed quasar
SDSS J1226-0006. We identify the system as a lensed quasar based on the
unresolved light curve and estimate a time delay in good agreement with the one
measured by COSMOGRAIL using the individual image light curves. The technique
shows great potential to identify lensed quasars in wide field imaging surveys,
especially the soon to be commissioned Vera Rubin Observatory.
