The Roman Space Telescope Relative Calibration System and the Dark Energy Figure of Merit

Abstract

One of the Roman Space Telescopes principal science objectives is to measure dark energy's equation-of-state using a strategic combination of imaging and spectroscopic surveys at high galactic latitude. Type Ia Supernovae survey requirements demand 0.3% photometric accuracy and calibration of key systematic effects. One of these is count rate dependent nonlinearity (CRNL) that if uncorrected affects the accuracy of SNe Ia distance measurements. Romans Relative Calibration System (RCS) enables on-orbit measurement and tracking of CRNL, through a direct illumination mode and a simultaneous lamp plus scene mode. We present results on the impact of CRNL calibration on the dark energy figure of merit (FoM), for a specific reduction of RCS capabilities. We examined many combinations of illumination and passbands, finding that only six meet the requirements. No RCS at all results in a factor of 5 degradation in the FoM.