Be It Unresolved: Measuring Time Delays from Lensed Supernovae

TL;DR

This paper develops a method to identify unresolved gravitationally lensed Type Ia supernovae and accurately measure their time delays using lightcurve data, enhancing their utility for cosmological studies.

Contribution

The authors introduce a novel technique to detect unresolved lensed supernovae and extract time delays with high accuracy, addressing a key challenge for upcoming surveys.

Findings

Successfully identifies unresolved lensed supernovae with low false positives.

Measures time delays with over 93% completeness and less than 0.5% bias for delays over 10 days.

Applicable to future large-scale time domain surveys for cosmology.

Abstract

Gravitationally lensed Type Ia supernovae may be the next frontier in cosmic probes, able to deliver independent constraints on dark energy, spatial curvature, and the Hubble constant. Measurements of time delays between the multiple images become more incisive due to the standardized candle nature of the source, monitoring for months rather than years, and partial immunity to microlensing. While currently extremely rare, hundreds of such systems should be detected by upcoming time domain surveys. Even more will have the images spatially unresolved, with the observed lightcurve a superposition of time delayed image fluxes. We investigate whether unresolved images can be recognized as lensed sources given only lightcurve information, and whether time delays can be extracted robustly. We develop a method that successfully identifies such systems, with a false positive rate of $\lesssim 5\%$, and measures the time delays with a completeness of $\gtrsim 93\%$ and with a bias of $\lesssim 0.5\%$ for $\Delta t_{\rm fit} \gtrsim 10$ days.