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Discovery of SN 2025wny: a Strongly Gravitationally Lensed Superluminous Supernova at z = 2.01

Joel Johansson, Daniel A. Perley, Ariel Goobar, Jacob L. Wise, Yu-Jing Qin, Zoë McGrath, Steve Schulze, Cameron Lemon, Anjasha Gangopadhyay, Konstantinos Tsalapatas, Igor Andreoni, Eric C. Bellm, Joshua S. Bloom, Richard Dekany, Suhail Dhawan, Christoffer Fremling, Matthew J. Graham, Steven L. Groom, Daniel Gruen, Xander J. Hall, Mansi Kasliwal, Russ R. Laher, Ragnhild Lunnan, Ashish A. Mahabal, Adam A. Miller, Edvard Mörtsell, Jakob Nordin, Jacob Osman Hjortlund, R. Michael Rich, Reed L. Riddle, Avinash Singh, Jesper Sollerman, Alice Townsend, Lin Yan

TL;DR

This work reports the discovery and ground-based characterization of SN 2025wny, the first gravitationally lensed Type I superluminous supernova (SLSN-I) at $z=2.011$, lensed by a foreground galaxy at $z_{ m lens}=0.357$ into four resolved images. Deep imaging resolves an Einstein Cross and spectroscopy from NOT and Keck establishes the host redshift, lens redshift, and the SLSN-I nature via UV features, while UV template comparisons and blackbody fits characterize the spectral properties and environment. The analysis infers a large lensing magnification of $\gtrsim 20$ and potentially up to $\sim 50$, enabling ground-based access to high-redshift SLSNe and offering a new window into distant dwarf hosts and time-delay cosmography. The finding underscores a rapidly growing role for lensed SNe in cosmology, with LSST and space missions like JWST and Euclid poised to expand the sample and precision of lens-model and cosmographic studies.

Abstract

We present the discovery of SN 2025wny (ZTF25abnjznp/GOTO25gtq) and spectroscopic classification of this event as the first gravitationally lensed Type I superluminous supernovae (SLSN-I). Deep ground-based follow-up observations resolves four images of the supernova with ~1.7" angular separation from the main lens galaxy, each coincident with the lensed images of a background galaxy seen in archival imaging of the field. Spectroscopy of the brightest point image shows narrow features matching absorption lines at a redshift of z = 2.011 and broad features matching those seen in superluminous SNe with Far-UV coverage. We infer a magnification factor of 20 to 50 for the brightest image in the system, based on photometric and spectroscopic comparisons to other SLSNe-I. SN 2025wny demonstrates that gravitationally-lensed SNe are in reach of ground-based facilities out to redshifts far higher than what has been previously assumed, and provide a unique window into studying distant supernovae, internal properties of dwarf galaxies, as well as for time-delay cosmography.

Discovery of SN 2025wny: a Strongly Gravitationally Lensed Superluminous Supernova at z = 2.01

TL;DR

This work reports the discovery and ground-based characterization of SN 2025wny, the first gravitationally lensed Type I superluminous supernova (SLSN-I) at , lensed by a foreground galaxy at into four resolved images. Deep imaging resolves an Einstein Cross and spectroscopy from NOT and Keck establishes the host redshift, lens redshift, and the SLSN-I nature via UV features, while UV template comparisons and blackbody fits characterize the spectral properties and environment. The analysis infers a large lensing magnification of and potentially up to , enabling ground-based access to high-redshift SLSNe and offering a new window into distant dwarf hosts and time-delay cosmography. The finding underscores a rapidly growing role for lensed SNe in cosmology, with LSST and space missions like JWST and Euclid poised to expand the sample and precision of lens-model and cosmographic studies.

Abstract

We present the discovery of SN 2025wny (ZTF25abnjznp/GOTO25gtq) and spectroscopic classification of this event as the first gravitationally lensed Type I superluminous supernovae (SLSN-I). Deep ground-based follow-up observations resolves four images of the supernova with ~1.7" angular separation from the main lens galaxy, each coincident with the lensed images of a background galaxy seen in archival imaging of the field. Spectroscopy of the brightest point image shows narrow features matching absorption lines at a redshift of z = 2.011 and broad features matching those seen in superluminous SNe with Far-UV coverage. We infer a magnification factor of 20 to 50 for the brightest image in the system, based on photometric and spectroscopic comparisons to other SLSNe-I. SN 2025wny demonstrates that gravitationally-lensed SNe are in reach of ground-based facilities out to redshifts far higher than what has been previously assumed, and provide a unique window into studying distant supernovae, internal properties of dwarf galaxies, as well as for time-delay cosmography.

Paper Structure

This paper contains 8 sections, 5 figures.

Table of Contents

  1. Introduction
  2. Observations
  3. Discovery of SN 2025wny
  4. Imaging
  5. Spectroscopy
  6. Spectral Analysis
  7. Light Curve Analysis and Magnification
  8. Conclusions

Figures (5)

  • Figure 1: RGB composite images of the lens system from Legacy Survey ($g$ and $z$-bands) and CFHT $R$-band imaging (left panel) prior to the SN explosion. The following panels show the Pan-STARRS images used for image subtraction, LT $gri$ images from 2025 October 4, and the right panel the four transient images of SN 2025wny.
  • Figure 2: Left panel: Public ZTF $g$ and $r-$band light curves of SN 2025wny, shown as green and red symbols. Black vertical lines indicate the time of the discovery, spectroscopic observations and our reported AstroNotes wise2025johansson2025. Right panel: Spectra of SN 2025wny (black lines) and the two galaxies forming the lens system (blue lines). Prominent absorption lines from the SN host galaxy at $z=2.011 \pm 0.001$, and the two lens galaxies at $z_{\rm lens}=0.3754$ are marked with vertical red and blue lines, respectively. The dashed green curves show blackbody fits to the SN spectra, with $T_{BB} \sim$29000, 23000 and 18000 K, for the three spectra.
  • Figure 3: Keck/LRIS spectrum of SN 2025wny (black line) compared to HST spectra of the low-$z$ SLSN-I 2016eay (a.k.a Gaia16apd, blue line), SN 2017egm (green line) and a Magellan/LDSS3 spectrum of high-$z$ DES16C2nm (red line). All spectra are scaled by their luminosity distance relative to SN 2025wny, and for clarity SNe 2016eay and 2017egm have been offset by multiplicative factors of 20 and 15, respectively.
  • Figure 4: Selection of absorption lines identified for SN 2025wny, used to determine the SN host redshift $z=2.011 \pm 0.001$.
  • Figure 5: Rest-frame UV light curve of Image A of SN 2025wny (from the ZTF $r$-band) compared to a set of comparison SLSN curves in similar rest-frame bands: SN 2017egm, SN 2016eay, PS1-13or, DES15E2mlf, and DES16C2nm. The observation times of the spectra used for the comparison in Figure \ref{['fig:slsn_comparison']} are marked with an "S".