Interpreting the strongly lensed supernova iPTF16geu: time delay predictions, microlensing, and lensing rates

TL;DR

This paper predicts time delays, examines microlensing effects, and estimates lensing rates for the strongly lensed supernova iPTF16geu, highlighting challenges in measuring delays and implications for cosmology.

Contribution

It provides detailed predictions of time delays, analyzes microlensing impacts, and assesses the likelihood of lensing events in the iPTF survey.

Findings

Maximum time delay less than a day consistent with observations

Most supernova images are affected by microlensing

Lensing rate in iPTF is likely high, but observed magnification exceeds expectations

Abstract

We present predictions for time delays between multiple images of the gravitationally lensed supernova, iPTF16geu, which was recently discovered from the intermediate Palomar Transient Factory (iPTF). As the supernova is of Type Ia where the intrinsic luminosity is usually well-known, accurately measured time delays of the multiple images could provide tight constraints on the Hubble constant. According to our lens mass models constrained by the {\it Hubble Space Telescope} F814W image, we expect the maximum relative time delay to be less than a day, which is consistent with the maximum of 100 hours reported by Goobar et al. but places a stringent upper limit. Furthermore, the fluxes of most of the supernova images depart from expected values suggesting that they are affected by microlensing. The microlensing timescales are small enough that they may pose significant problems to measure the time delays reliably. Our lensing rate calculation indicates that the occurrence of a lensed SN in iPTF is likely. However, the observed total magnification of iPTF16geu is larger than expected, given its redshift. This may be a further indication of ongoing microlensing in this system.