Calibration

In SNe Ia cosmology, there are specific calibration requirements that will limit uncertainties in certain quantities (such as w_0 and wb_a). These calibration uncertainties are the largest aspect of the SNe FoM error budget. We plan to fulfill these specific requirements that pertain to our SNe Ia cosmological analysis.

SNe Ia cosmology requires strict calibration requirements, some of which include (for photometry) 0.3% accuracy over 11 mag in brightness and 0.5% for the absolute color between 0.7μm-2μm. We plan to expand upon the standard calibrations preformed by SOC, as the SOC pipeline does not have any formal accuracy requirements. We are working to use resources outside of the Ground System to fulfill the specific calibration requirements by completing the following:

  • Characterize and mitigate the detector effects to be 0.3% over 11 mags

    • We will collaborate with the Roman Project and the SOC to develop an analysis procedure to obtain a pre-launch characterization of the count rate non-linearity (CRNL).

    • We will additionally work with the SOC and use dedicated calibration programs (CFA and Lamp-on/Lamp-off method) and complete the ultimate measurement of count-rate dependent non-linearity.

  • Characterize passband throughputs as well as their field dependence to 1 Å

    • We will work in collaboration with the Roman Project, the SOC, and the SSC to characterize the position-dependent filter passbands.

      • We will need to solve for the position dependence of the instrument throughput against the wavelength.

    • We will also characterize the bandpasses of the full system with the goal of a 1 Å uncertainty on the effective wavelength for each filter.

  • Constrain the prism spectral response across the observing field to be 0.2% per 5000 Å

    • We will work with the analysis of the lab testing pre-launch and work to develop algorithms for characterizing the spectral response for the post-launch.

  • Propagate the calibrated spectroscopy of primary standards to 1 mmag

    • Based on primary standards that are newly developed by the community, we will leverage the absolute flux calibration to complete the following:

      • We plan to build a calibration ladder across wavelength and magnitude.

      • We will also establish a system for photometry and spectroscopy of stellar sources (of tertiary standards).

  • Develop an error covariance matrix

    • We will provide an error covariance matrix for the SN Ia community which will include a wavelength-dependent matrix that is suited for photometry and spectroscopy and will also aid in cosmological fitting.

    • We will use error estimates and covariance matrices to improve and develop our analysis tools and assessments of observing strategies.