Identifying Lensed Quasars and Measuring Their Time Delays from Unresolved Light Curves

Abstract

Abstract Identifying multiply imaged quasars is challenging owing 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 telescope, we find that precision can remain close to 100% while recall drops to ∼60%. We also consider some examples from Time Delay Challenge 1 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.