Identifying lensed quasars and measuring their time-delays from unresolved light curves

TL;DR

This paper presents a novel method to identify lensed quasars and measure their time delays using unresolved light curves, enabling detection without high-resolution imaging and applicable to large sky surveys.

Contribution

The authors introduce a new technique that detects lensed quasars and estimates time delays solely from unresolved light curves, bypassing the need for prior templates or high-resolution data.

Findings

High precision and recall achievable with low-noise data

Method remains effective with noise levels similar to ZTF

Accurate time delay recovery demonstrated on real data

Abstract

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.