Detection of the Gravitational Lens Magnifying a Type Ia Supernova

TL;DR

This paper reports the first detection of a gravitational lens magnifying a Type Ia supernova, confirmed by spectral evidence of a foreground galaxy, opening new possibilities for using lensed supernovae to measure cosmic expansion.

Contribution

It provides the first spectroscopic confirmation of a gravitational lens magnifying a Type Ia supernova, demonstrating the potential to identify more such events for cosmological studies.

Findings

First confirmed case of a lensed Type Ia supernova

Spectroscopic evidence of a foreground galaxy

Potential for discovering more lensed supernovae

Abstract

Objects of known brightness, like Type Ia supernovae (SNIa), can be used to measure distances. If a massive object warps spacetime to form multiple images of a background SNIa, a direct test of cosmic expansion is also possible. However, these lensing events must first be distinguished from other rare phenomena. Recently, a supernova was found to shine much brighter than normal for its distance, which resulted in a debate: was it a new type of superluminous supernova or a normal SNIa magnified by a hidden gravitational lens? Here we report that a spectrum obtained after the supernova faded away shows the presence of a foreground galaxy--the first found to strongly magnify a SNIa. We discuss how more lensed SNIa may be found than previously predicted.