Projected Cosmological Constraints from Strongly Lensed Supernovae with the Roman Space Telescope

TL;DR

This paper forecasts the potential of the Roman Space Telescope to constrain dark energy parameters through observations of strongly lensed supernovae, providing tools and strategies for future cosmological studies.

Contribution

It introduces a method to forecast lensed supernova constraints with Roman, including mock catalogs and analysis tools, highlighting an optimized survey strategy for high-redshift supernova discovery.

Findings

Roman will detect approximately 11 lensed SNIa and 20 CCSN.

Time delay measurements will have a precision of about 2-3 days.

Optimized survey strategy enhances constraints on dark energy parameters.

Abstract

One of the primary mission objectives for the Roman Space Telescope is to investigate the nature of dark energy with a variety of methods. Observations of Type Ia supernovae (SNIa) will be one of the principal anchors of the Roman cosmology program, through traditional luminosity distance measurements. This SNIa cosmology program can provide another valuable cosmological probe, without altering the mission strategy: time delay cosmography with gravitationally lensed SN. In this work, we forecast lensed SN cosmology constraints with the Roman Space Telescope, while providing useful tools for future work. Using anticipated characteristics of the Roman SNIa survey, we have constructed mock catalogs of expected resolved lensing systems, as well as strongly lensed Type Ia and core-collapse (CC) SN light curves, including microlensing effects. We predict Roman will find ~11 lensed SNIa and ~20 CCSN, dependent on the survey strategy. Next, we estimate the time delay precision obtainable with Roman (Ia: ~2 days, CC: ~3 days), and use a Fisher matrix analysis to derive projected constraints on $H_0$,$\Omega_m$, and the dark energy Equation of State (EOS), $w$, for each SNIa survey strategy. A strategy optimized for high-redshift SNIa discovery is preferred when considering the constraints possible from both SNIa and lensed SN cosmology, also delivering ~1.5 times more lensed SN than other proposed survey strategies.