Lensed Type Ia Supernova "Encore" at z=2: The First Instance of Two Multiply-Imaged Supernovae in the Same Host Galaxy

TL;DR

This paper reports the discovery of the second multiply-imaged Type Ia supernova in the same host galaxy, using JWST data, which offers new opportunities for measuring the Hubble Constant and studying gravitational lensing.

Contribution

It presents the first case of two multiply-imaged SNe Ia in the same host galaxy, demonstrating the potential for precise cosmological measurements with lensed supernovae.

Findings

Discovery of SN Encore, a second multiply-imaged SN Ia in the same galaxy.

First system known to produce more than one multiply-imaged SN.

Potential to measure Hubble Constant with ~10% precision using this system.

Abstract

A bright ($m_{\rm F150W,AB}$=24 mag), $z=1.95$ supernova (SN) candidate was discovered in JWST/NIRCam imaging acquired on 2023 November 17. The SN is quintuply-imaged as a result of strong gravitational lensing by a foreground galaxy cluster, detected in three locations, and remarkably is the second lensed SN found in the same host galaxy. The previous lensed SN was called "Requiem", and therefore the new SN is named "Encore". This makes the MACS J0138.0$-$2155 cluster the first known system to produce more than one multiply-imaged SN. Moreover, both SN Requiem and SN Encore are Type Ia SNe (SNe Ia), making this the most distant case of a galaxy hosting two SNe Ia. Using parametric host fitting, we determine the probability of detecting two SNe Ia in this host galaxy over a $\sim10$ year window to be $\approx3\%$. These observations have the potential to yield a Hubble Constant ($H_0$) measurement with $\sim10\%$ precision, only the third lensed SN capable of such a result, using the three visible images of the SN. Both SN Requiem and SN Encore have a fourth image that is expected to appear within a few years of $\sim2030$, providing an unprecedented baseline for time-delay cosmography.