Holismokes

Abstract

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.

Holismokes

“…where D s is the angular-diameter distance from the observer to the source, D ds the angular-diameter distance from the lens to the source, D d the angular-diameter distance from the observer to the lens, and c the speed of light. We further assumed a Salpeter initial mass function with a mean mass of the point mass microlenses of M = 0.35M as described by Huber et al (2021). The magnification maps are primarily defined by three parameters: the convergence κ, the shear γ, and the smooth matter fraction s = 1 − κ * κ , where κ * is the convergence of the stellar component.…”

“…1 The type I and II refer to the types of lensing images, not SN types. we chose κ = 0.7 and γ = 0.7, which are the median values of type II lensing images of the OM10 catalog (Huber et al 2021;Suyu et al 2020). We adopted s = 0.5 for both cases.…”

“…Even though the non-microlensed light curves are almost linear, which leads to nearly linear color curves, we wanted to show the influence of microlensing on these color curves, following Goldstein et al (2018), Huber et al (2019Huber et al ( , 2021. Due to the achromatic specific intensity profiles, the influence is expected to be low.…”

“…This causes the spectrum to be magnified to an unknown amount and makes time-delay measurements difficult. Goldstein et al (2018), Huber et al (2021) show that microlensing of LSNe Ia is mostly achromatic. In three of five color curves, Huber et al (2021) find characteristic minima or maxima within the achromatic phase of SNe Ia, making time-delay measurements with LSNe Ia feasible.…”

“…Several lensing studies on SN Refsdal have been performed (e.g., Rodney et al 2016;Kelly et al 2016b;Treu et al 2016;Pierel & Rodney 2019;Grillo et al 2016Grillo et al , 2020Baklanov et al 2021); iPTF16geu has been studied extensively (Goobar et al 2017;More et al 2017;Yahalomi et al 2017;Dhawan et al 2018;Johansson et al 2021) and shows strong signs of microlensing. Further studies on SNe Ia and their usability to measure time delays have been conducted by Goldstein et al (2018), Foxley-Marrable et al (2018), Huber et al (2019Huber et al ( , 2021. The main focus of those papers has been the characterization of the perturbations introduced by microlensing.…”