Microlensing and the type Ia supernova iPTF16geu

TL;DR

This study uses observations of the quadruply-imaged supernova iPTF16geu to constrain lens models, demonstrating that microlensing by stars explains the flux ratios and light curves without needing additional substructures.

Contribution

It introduces a combined macro+micro lens modeling approach using light curves and magnifications, providing new constraints on stellar mass contributions in lensing galaxies.

Findings

Microlensing explains observed flux ratios and light curves.

Larger stellar surface mass densities are favored.

Baryonic mass is dominated by stellar component.

Abstract

The observed magnifications and light curves of the quadruply-imaged iPTF16geu supernova (SN) offers a unique opportunity to study a lens system with a variety of independent constraints. The four observed positions can be used to constrain the macrolens model. The magnifications and light curves at the four SN positions are more useful to constrain microlensing models. We define the macrolens model as a combination of a baryonic component that traces the observed light distribution, and a dark matter halo component. We constrain the macrolens model using the positional constraints given by the 4 observed images, and compare it with the best model obtained when magnification constraints are included. We find that the magnification can not be explained by a macrolens model alone, and that contributions from substructures such as microlenses are needed to explain the observed magnifications. We consider microlens models based on the inferred stellar mass from the baryonic component of the macrolens model, and use the observed magnification and light curves to constrain the contribution from microlenses. We compute the likelihood of a variety of macro+micro lens models where we vary the dark matter halo, baryonic component, and microlens configurations. We use information about the position, magnification and, for the first time, the lightcurves of the four observed SN images. We combine macrolens and microlens models in order to reproduce the observations; the four SN positions, magnifications, and lack of fluctuations in the light curves. After marginalizing over the model parameters, we find that larger stellar surface mass densities are preferred. This result suggests that the mass of the baryonic component is dominated by its stellar component. We conclude that microlensing from the baryonic component suffices to explain the observed flux ratios and light curves.