To use strongly lensed Type Ia supernovae (LSNe Ia) for cosmology, a time-delay measurement between the multiple supernova (SN) images is necessary. The sharp rise and decline of SN Ia light curves make them promising for measuring time delays, but microlensing can distort these light curves and therefore add large uncertainties to the measurements. An alternative approach is to use color curves where uncertainties due to microlensing are significantly reduced for a certain period of time known as the achromatic phase. In this work, we investigate in detail the achromatic phase, testing four different SN Ia models with various microlensing configurations. We find on average an achromatic phase of around three rest-frame weeks or longer for most color curves, but the spread in the duration of the achromatic phase (due to different microlensing maps and filter combinations) is quite large and an achromatic phase of just a few days is also possible. Furthermore, the achromatic phase is longer for smoother microlensing maps and lower macro-magnifications. From our investigations, we do not find a strong dependency on the SN model or on asymmetries in the SN ejecta. We find that six rest-frame LSST color curves exhibit features such as extreme points or turning points within the achromatic phase, which make them promising for time-delay measurements; however, only three of the color curves are independent. These curves contain combinations of rest-frame bands u, g, r, and i, and to observe them for typical LSN Ia redshifts, it would be ideal to cover (observer-frame) filters r, i, z, y, J, and H. If follow-up resources are restricted, we recommend r, i, and z as the bare minimum for using color curves and/or light curves since LSNe Ia are bright in these filters and observational uncertainties are lower than in the infrared regime. With additional resources, infrared observations in y, J, and H would be useful for obtaining color curves of SNe, especially at redshifts above ∼0.8 when they become critical.
Bibliographical noteFunding Information:
Acknowledgements. We thank M. Oguri and P. Marshall for the useful lens catalog from Oguri & Marshall (2010), and W. Hillebrandt, S. Blondin, D. A. Goldstein for useful discussions. We also would like to thank the anonymous referee for helpful comments, which strengthened this work. SH and SHS thank the Max Planck Society for support through the Max Planck Research Group for SHS. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (LENSNOVA: grant agreement No 771776; COSMICLENS: grant agreement No 787886). This research is supported in part by the Excellence Cluster ORIGINS which is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2094 – 390783311. UMN has been supported by the Transregional Collaborative Research Center TRR33 ‘The Dark Universe’ of the Deutsche Forschungsgemeinschaft. JHHC acknowledges support from the Swiss National Science Foundation and through European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (COS-MICLENS: grant agreement No 787866). MK acknowledges support from the Klaus Tschira Foundation.
© S. Huber et al. 2021.
Copyright 2021 Elsevier B.V., All rights reserved.
- Cosmology: observations
- Gravitational lensing: micro
- Gravitational lensing: strong
- Supernovae: individual: Type Ia
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science