Microlensing and the type Ia supernova iPTF16geu
  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.
