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AI summary · arXiv: 2610.33161v1 · astro-ph.HE

SN Ares: A Strongly Lensed Type IIb Supernova at $\mathbf{z=1.276}$ with a Predicted 70-Year Time Delay

Conor Larison, Justin D. R. Pierel, Matthew Siebert, Tom Resseguier, Lukas J. Furtak, Masamune Oguri, Gavin S. Farley, Hollis B. Akins,
and 64 more authorsYoshihisa Asada, Rachel Bezanson, Maruša Bradač, Gabriel Brammer, John Chisholm, Dan Coe, Pratika Dayal, Henry C. Ferguson, Steven L. Finkelstein, Seiji Fujimoto, Tomokazu Kiyota, Anton M. Koekemoer, Vasily Kokorev, Minami Nakane, Masami Ouchi, Richard Pan, Casey Papovich, Johan Richard, Luke Robbins, Fengwu Sun, Kana Takechi, Tommaso Treu, Chris Willott, Hiroto Yanagisawa, Abdurro'uf, Joseph F. V. Allingham, Ricardo O. Amorín, Franz E. Bauer, Larry Bradley, Mateusz Bronikowski, Christopher J. Conselice, David A. Coulter, James M. DerKacy, José M. Diego, Eiichi Egami, Andreas L. Faisst, Ori D. Fox, Brenda L. Frye, Yoshinobu Fudamoto, Mauro González-Otero, Massimo Griggio, Nimish P. Hathi, Tiger Yu-Yang Hsiao, Saurabh W. Jha, Y. Jiménez-Teja, Jeyhan S. Kartaltepe, Gourav Khullar, Zachary G. Lane, Paulo A. A. Lopes, Ray A. Lucas, Georgios E. Magdis, Matteo Messa, Rohan P. Naidu, Rafael Ortiz, Massimo Pascale, Armin Rest, Massimo Ricotti, Melissa Shahbandeh, William Sheu, Koji Shukawa, Rogier A. Windhorst, Anita Zanella, Yossef Zenati, Adi Zitrin
Original paper Submitted to arXiv on 23 Oct. 2026 22 pages, 12 figures, 4 tables, submitted to ApJ License: CC BY 4.0 Also in: fr

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The essentials

JWST observations identify SN Ares as a strongly lensed Type IIb supernova at z=1.276, with its next images predicted to arrive roughly 70 years later.

Question

The paper asks what type and evolutionary phase SN Ares is, and what its discovery implies for studying high-redshift supernovae and future time-delay cosmography. It also estimates when the other lensed images may appear.

Method

The authors analyze JWST/NIRCam imaging and NIRSpec spectroscopy, supported by HST observations, to measure the redshift, classify the supernova, and compare its spectrum and light curve with local Type IIb supernovae. They use three independent cluster lens models; the models draw on 45–48 multiple images and predict future arrivals about 70–79 years after the observed image. Light-curve fits use three local analogs and a Type IIb population template.

Findings

  • Result Emission-line measurements give SN Ares a spectroscopic redshift of 1.276 ± 0.002.
    See the passage in the paper
    The best fit is z = $1.276\pm 0.002$.
  • Authors’ interpretation Hydrogen and helium features, including their relative strengths, support classifying SN Ares as a Type IIb supernova.
    See the passage in the paper
    From this, we found that the best classification is that of a Type IIb SN (SN IIb)
  • Result Photometric comparisons place the second JWST epoch about 31–34 rest-frame days after the radioactive B-band peak.
    See the passage in the paper
    From these template fits to SNe 1993J, 2011dh, 2011fu and the population-level templates, we recover a phase estimate for the second epoch of JWST data (e.g. our spectral phase) of $31_{-5}^{+11}$, $34_{-5}^{+10}$, $31_{-9}^{+13}$, and $34_{-9}^{+10}$ days, respectively.
  • Result The three lens models predict later images approximately 70–79 years after the observed image, with magnifications of roughly 1.5–4.9 for the later appearances.
    See the passage in the paper
    According to this model, SN Ares is magnified by a factor $\mu=4.6\pm 0.4$, in agreement with both the lenstool and glafic models at $1\sigma$, and will re-appear in $76.4\pm 0.3$ yr, and again in $79.1\pm 0.4$ yr.
  • Authors’ interpretation The authors argue that capturing a future reappearance could provide a highly precise time-delay measurement, although its cosmological usefulness depends on lens-model systematics.
    See the passage in the paper
    The usefulness of SN Ares for cosmology will be limited only by the systematics in the lens models themselves.

Limitations

  • Current lens-model predictions have substantial image-position reproduction errors, and the authors expect future JWST spectroscopy to improve the constraints.
    See the passage in the paper
    The lens model has an RMS of $0.^{\prime\prime}66$ and was used to estimate $\mu=5.6\pm 0.5$ for SN Ares.
  • Residual host-galaxy emission may affect the measured H-alpha profile, limiting constraints on the supernova's hydrogen envelope.
    See the passage in the paper
    Residual host-galaxy emission may contribute to the observed H$\alpha$ profile, making differences in hydrogen envelope mass poorly constrained given the current dataset.
  • The study presents one event, so it cannot establish whether supernova populations or progenitor channels have evolved at high redshift.
    See the passage in the paper
    Its broad resemblance to nearby analogs shows that familiar SN IIb spectral behavior can be identified at this redshift, although a single event cannot establish whether the population or its progenitor channels have evolved.

Why it matters

The authors present SN Ares as evidence that targeted JWST observations of massive clusters can enable detailed spectroscopic study of distant, lensed supernovae. Its exceptionally long predicted delays could make it a valuable future cosmography target, while the present predictions remain limited by lens-model systematics.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: SN Ares; Type IIb supernova; gravitational lensing; JWST; time delays

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  • Original abstract
The paper reports the discovery and analysis of SN Ares, a strongly gravitationally lensed Type IIb supernova in a multiply imaged host galaxy behind the galaxy cluster MACS J0308.9+2645. The study investigates Ares’s supernova type, its evolutionary phase when observed, and whether the cluster lens could produce later images useful for measuring time delays and studying cosmology. Ares was discovered in JWST/NIRCam images taken on August 23, 2025. About a month later, it was observed with JWST/NIRSpec spectroscopy and additional imaging. From the host galaxy’s emission lines, the authors measured a redshift of 1.276 ± 0.002. They classified the supernova by comparing its spectrum with those of local core-collapse supernovae using a method that accounts for residual host-galaxy light. They estimated its phase by comparing both its spectrum and JWST photometry with local Type IIb supernovae and population-level light-curve templates. For the lensing analysis, they used three independent cluster models based on multiply imaged background sources. The spectrum shows helium features near 5876, 7065, and 10,830 angstroms, as well as hydrogen-alpha and Paschen-beta. The strength and combination of these features support a Type IIb classification: an explosion of a massive star that retained some hydrogen but had lost much of its outer envelope. According to the paper, Ares is the highest-redshift Type IIb supernova identified spectroscopically. Spectral comparisons provide broad estimates of Ares’s phase. Fits to the light curves of three local analogs—SN 1993J, SN 2011dh, and SN 2011fu—and to a Type IIb population template place the NIRSpec observation about 31–34 rest-frame days after the radioactive B-band peak. The population-template estimate is 34 days, with uncertainties of −9 and +10 days. The local analog fits are consistent with this estimate. SN 1993J is the closest overall comparison, although Ares appears to have stronger hydrogen-alpha and a weaker calcium infrared triplet. The authors caution that phase differences and host-galaxy contamination could contribute to these discrepancies. The lens models estimate Ares’s magnification at approximately 4.6–5.6. Using one model’s estimate of 5.6 ± 0.5, the authors infer an unlensed peak B-band absolute magnitude of roughly −17.1 to −17.9. This range is consistent with known nearby Type IIb supernovae and does not indicate that Ares is unusually bright. All three lens models predict that the currently observed image arrived first, followed by two additional images roughly 70–79 years later. In representative predictions, the later images have magnifications of approximately 5 and 1.5. The authors conclude that Ares demonstrates JWST’s ability to study distant supernovae made observable by cluster lensing, and that its future images could enable an unusually long-baseline time-delay measurement. Several limitations remain. The lens models are preliminary and have substantial image-position residuals; planned improved spectroscopy of the cluster’s multiply imaged systems could change the predicted delays and magnifications. Residual host-galaxy light affects the supernova spectrum, and a nearby bright star prevents useful HST detections. The phase estimates also rely on sparse photometry and comparisons with local events. Finally, a single supernova cannot establish whether progenitors or supernova populations evolve with redshift.
Created on 03 Nov. 2026

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