Microlensing of lensed supernovae Zwicky & iPTF16geu: constraints on the lens galaxy mass slope and dark compact object fraction

TL;DR

This study uses observations and simulations of two strongly lensed supernovae to constrain the mass distribution and dark compact object fraction in lens galaxies, finding no significant dark matter compact objects.

Contribution

It provides the first combined analysis of microlensing effects on lensed supernovae to constrain galaxy mass profiles and dark matter compact object fractions.

Findings

Mass slopes are approximately 1.7 and 1.8 for the two systems.

No evidence for a significant population of dark compact objects.

Upper limits on dark compact object fraction are below 0.25 and 0.47 at 95% confidence.

Abstract

To date, only two strongly lensed type Ia supernovae (SNIa) have been discovered with an isolated galaxy acting as the lens: iPTF16geu and SN Zwicky. The observed image fluxes for both lens systems were inconsistent with predictions from a smooth macro lens model. A potential explanation for the anomalous flux ratios is microlensing: additional (de)magnification caused by stars and other compact objects in the lens galaxy. In this work, we combine observations of iPTF16geu and SN Zwicky with simulated microlensing magnification maps, leveraging their standardizable candle properties to constrain the lens galaxy mass slope, $\eta$, and the fraction of dark compact objects, $f_{\rm dc}$. The resulting mass slopes are $\eta = 1.70 \pm 0.07$ for iPTF16geu and $\eta = 1.81 \pm 0.10$ for SN Zwicky. Our results indicate no evidence for a population of dark compact objects, placing upper limits at the $95\%$ confidence level of $f_{\rm dc} < 0.25$ for iPTF16geu and $f_{\rm dc} < 0.47$ for SN Zwicky (for compact objects with masses above $ 0.02 M_{\odot}$). Assuming a constant fraction of dark compact objects for both lensed SNe, we obtain $f_{\rm dc} < 0.19$. These results highlight the potential of strongly lensed SNIa to probe the innermost parts of lens galaxies and learn about compact matter.