pith. sign in

arxiv: 2604.11882 · v1 · submitted 2026-04-13 · 🌌 astro-ph.CO · astro-ph.GA

SN 2022riv in RX J2129: Discovery, Spectroscopic Classification, and Microlensing of a Strongly Lensed Type Ia Supernova from JWST and HST Observations

Birendra Dhanasingham , Patrick L. Kelly , Wenlei Chen , Justin Pierel , Masamune Oguri , Derek Perera , Jose M. Diego , Adi Zitrin
show 22 more authors
Ashish K. Meena Mathilde Jauzac Guillaume Mahler Elias Mamuzic Liliya L.R. Williams Yoon Chan Taak Anton M. Koekemoer Thomas J. Broadhurst Lukas J. Furtak David Lagattuta Hayley Williams Kyle Dalrymple Alexei V. Filippenko Christa Gall Daniel Gilman Jens Hjorth Saurabh W. Jha Conor Larison Chien-Hsiu Lee Paolo A. Mazzali Keren Sharon Sherry H. Suyu
This is my paper

Pith reviewed 2026-05-10 15:58 UTC · model grok-4.3

classification 🌌 astro-ph.CO astro-ph.GA
keywords strongly lensed supernovaType Ia supernovagravitational microlensingmagnification measurementJWST spectroscopyHST observationsgalaxy cluster lensinglight-curve fitting
0
0 comments X

The pith

A strongly lensed Type Ia supernova at z=1.522 yields a cosmology-independent magnification of 5.35 for its final image.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents the discovery of SN 2022riv in a multiply imaged galaxy lensed by the cluster RX J2129.7+0005, followed by spectroscopic confirmation as a Type Ia supernova using JWST NIRSpec data. Light-curve fitting with SALT3-NIR extracts the magnification of the last-to-arrive image directly from the observations. This approach tests predictions from six independent lens models while incorporating expected microlensing from the high stellar density near the brightest cluster galaxy. The result offers an independent check on cluster mass distributions that does not rely on cosmological assumptions.

Core claim

JWST and HST observations classify SN 2022riv as a Type Ia supernova in the last-to-arrive image of a z=1.522 galaxy. The SALT3-NIR fitter applied to its light curve measures a magnification of 5.35±1.01. Four of six lens models predict this value with higher precision than random chance would suggest, and five models give magnifications of 4-7 before microlensing correction. After nominal microlensing adjustment, most align with the measurement while one model remains in tension.

What carries the argument

The SALT3-NIR light-curve fitter applied to the supernova's multi-epoch photometry and spectroscopy to extract magnification.

If this is right

  • The measured magnification constrains the mass distribution in the foreground cluster RX J2129.
  • Microlensing must be modeled to reconcile lens predictions in high stellar-density regions near the brightest cluster galaxy.
  • Multiple lens models can be tested for consistency using lensed supernovae as standard candles.
  • The same method can be applied to future lensed Type Ia events for independent checks on strong-lensing models.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This measurement provides a test case for whether microlensing predictions improve agreement among different lens modeling techniques in dense cluster environments.
  • Repeated applications to other lensed supernovae could help identify systematic differences between lens models without assuming a cosmology.
  • The location's high stellar density offers a natural laboratory for studying how microlensing affects supernova light curves in real observations.

Load-bearing premise

The SALT3-NIR light-curve models accurately represent the supernova behavior without significant bias from microlensing or other systematics, and the spectroscopic classification as Type Ia is unambiguous.

What would settle it

An independent magnification estimate from time-delay measurements between the supernova images or from another lensing method that falls well outside the 4.34-6.36 range would falsify the reported value.

Figures

Figures reproduced from arXiv: 2604.11882 by Adi Zitrin, Alexei V. Filippenko, Anton M. Koekemoer, Ashish K. Meena, Birendra Dhanasingham, Chien-Hsiu Lee, Christa Gall, Conor Larison, Daniel Gilman, David Lagattuta, Derek Perera, Elias Mamuzic, Guillaume Mahler, Hayley Williams, Jens Hjorth, Jose M. Diego, Justin Pierel, Keren Sharon, Kyle Dalrymple, Liliya L.R. Williams, Lukas J. Furtak, Masamune Oguri, Mathilde Jauzac, Paolo A. Mazzali, Patrick L. Kelly, Saurabh W. Jha, Sherry H. Suyu, Thomas J. Broadhurst, Wenlei Chen, Yoon Chan Taak.

Figure 1
Figure 1. Figure 1: The HST WFC3/IR image of the RX J2129 galaxy cluster with three marked images (S1, S2, and S3) of the SN 2022riv host galaxy with the positions of the SN indicated. From top to bottom in the right-hand panels we show close-up views of the observation centered on the SN location taken by the CLASH survey in 2011 using the WFC3/IR F110W filter, the observation under the SNAP program on August 7, 2022 (S3, al… view at source ↗
Figure 2
Figure 2. Figure 2: The JWST NIRCam image of the RX J2129 galaxy cluster. The stamp image superposed on the main image shows the detected SN and its host galaxy, where green rectangles mark the open MSA shutters used in the NIRSpec MOS observations. tral absorption and emission features. These features were then cross-correlated with the SNID template li￾brary (“template 2.0”) using the correlation techniques of Tonry & Davis… view at source ↗
Figure 3
Figure 3. Figure 3: NIRSpec G140M spectra of the host galaxy (top, G140M/070LP; bottom, G140M/100LP). Blue vertical dashed lines indicate the positions of the detected emission lines. Wavelengths are shown in both the observed frame (bottom) and the rest frame at z = 1.522 (top). The shaded colored regions in both panels represent the uncertainty in the flux-density measurements. The gap in the G140M/070LP spectrum (top) near… view at source ↗
Figure 4
Figure 4. Figure 4: NIRSpec G140M/100LP (top) and CLEAR/PRISM (bottom) spectra of SN 2022riv used for the SNID analysis (black line). The 200 best-matching SN Ia templates from SNID are overlaid in cyan, with key spectral features labeled, confirming SN 2022riv as a Type Ia SN. This fitting interval was chosen to be as small as pos￾sible to minimize the effect of adjacent absorption fea￾tures. Finally, we repeated this fittin… view at source ↗
Figure 5
Figure 5. Figure 5: Left: JWST/NIRCam images in the F150W fil￾ter, showing SN 2022riv from the 2022 observation (top) and the 2025 visit to the cluster under the VENUS program (Oc￾tober 2025). Right: Difference images created from F150W and F444W observations taken during the 2022 October visit and the 2025 October visit to the cluster field. All images are drizzled to a pixel scale of 0. ′′03 pixel−1 and cover the same spati… view at source ↗
Figure 6
Figure 6. Figure 6: Maximum-likelihood light curves for each SN subclass obtained using Bayesian model selection based on the photometric data from HST and JWST. The black points with error bars indicate the observed photometry of SN 2022riv. The SN Ia model, shown by a red solid line, is based on the SALT3-NIR template at z = 1.522, with the F444W observation excluded from the plot since it falls outside the model’s waveleng… view at source ↗
Figure 7
Figure 7. Figure 7: Joint posterior distribution of the SALT light-curve parameters t0, x0, x1, and c obtained by fitting the light curves of SN 2022riv using four different SALT models in sncosmo, with key parameters and Bayesian evidence estimated via a nested sampling algorithm. The contours represent the 68% and 95% confidence intervals. rameters α and β describe the stretch–luminosity and color–luminosity relationships, … view at source ↗
Figure 8
Figure 8. Figure 8: Comparison of the inferred distance modulus of SN 2022riv (red data points) with the distance moduli for our sample of unlensed field SNe (gray data points) for each SALT light curve fitter. The black line, anchored at the redshift of SN 2022riv, represents the best linear fit to the unlensed control sample, with the gray-shaded region indicating the associated 1σ error. The best-fit linear relationships f… view at source ↗
Figure 9
Figure 9. Figure 9: SED fitting results for the ICL region at the po￾sitions of SN 2022riv Image S3, obtained using Prospector. The filled orange circles with error bars indicate the JWST photometric data. The best-fit model is shown in blue, with a solid line representing the SED fit and squares denoting the predicted photometry from the model. 7.03+0.21 −0.33 and 7.35+0.17 −0.29 for Image S1 and S2, respec￾tively), with Ima… view at source ↗
Figure 10
Figure 10. Figure 10: The PDFs of the change in WFC3/IR F160W magnitude for each lens model and each Type Ia SN explosion model due to stellar microlensing. The blue (red) histograms represent the PDFs from microlensing simulations using the Chabrier (Salpeter) IMF. Dotted vertical lines indicate the median value for each case, while the shaded color bands represent the 16th and 84th percentiles. The scatter, σML, is shown on … view at source ↗
Figure 11
Figure 11. Figure 11: The PDFs of the absolute magnifications for each lens model and each SN Ia explosion model, after correcting the initial absolute magnification estimates from lens modelling (µmodel) for stellar microlensing and dark matter substructure millilensing. The blue (red) curves represent the PDFs derived assuming the Chabrier (Salpeter) IMF in the microlensing simulations. Dotted vertical lines indicate the med… view at source ↗
Figure 12
Figure 12. Figure 12: Flattened G140M/100LP spectrum of SN 2022riv used for the SNID analysis (black line). The 23 best-matching SN Ib templates (green curves in the top panel) and 30 best-fitting SN Ic templates (blue curves in the bottom panel) with r × lap > 5 from SNID are shown for comparison. No SN II template matches were found. Arendse, N., M¨ortsell, E., Weisenbach, L., et al. 2025, The Open Journal of Astrophysics, 8… view at source ↗
Figure 13
Figure 13. Figure 13: Same as in [PITH_FULL_IMAGE:figures/full_fig_p028_13.png] view at source ↗
Figure 14
Figure 14. Figure 14: Cutout images of the newly identified systems S3-(1–2)a, S3-(1–2)b, and S3-(1–2)c, all with spectroscopic redshifts of z = 1.5194, as detected and localized using JWST NIRCam observations [PITH_FULL_IMAGE:figures/full_fig_p029_14.png] view at source ↗
Figure 15
Figure 15. Figure 15: Cutout images showing prospective multiple￾image candidates in the RX J2129 galaxy cluster field. Sys￾tem 11 is well localized using JWST/NIRCam observations. Systems 10 and 12 are not clearly identifiable owing to their extended and complex morphologies. Dashed circles indicate the inferred positions of these systems. Bonvin, V., Tihhonova, O., Millon, M., et al. 2019, A&A , 621, A55, doi: 10.1051/0004-6… view at source ↗
Figure 16
Figure 16. Figure 16: The same as in [PITH_FULL_IMAGE:figures/full_fig_p032_16.png] view at source ↗
read the original abstract

The multiply imaged SN 2022riv was discovered through a search of galaxy cluster fields as part of a Hubble Space Telescope (HST) SNAP program to find highly magnified stars. The supernova (SN) was detected in the last-to-arrive image of a galaxy at redshift $z=1.522$ strongly lensed by the foreground galaxy cluster RX J2129.7+0005. Follow up James Webb Space Telescope (JWST) NIRSpec G140M and PRISM spectroscopy yields a Type Ia SN classification. Using the SALT3-NIR light-curve fitter, we obtain a cosmology-independent measurement of the magnification of $5.35\pm1.01$ for the last-to-arrive image of the SN, with multiple SALT SN spectral time-series models yielding consistent constraints. The last-to-arrive image of SN 2022riv we detect appeared adjacent to the brightest cluster galaxy (BCG) at a location with an exceptionally high stellar mass density ($\sim 1-2$ dex higher than that of SN Refsdal), where microlensing is expected to introduce a 20-50% modulation of the magnification. Analyzing six independent lens models of the cluster, we find that four predict the magnification with much greater precision ($p < 0.05$) than would be expected by random chance, given the large effect anticipated from microlensing. Five models yield magnifications of roughly $4-7$ (within $1\sigma$) prior to accounting for microlensing, whereas HoliGRALE favors a significantly higher value of $15.39 \pm 0.85$. After incorporating nominal microlensing, the HoliGRALE prediction is within $1\sigma$ tension with our measurement. A companion paper (Dalrymple et al.) will present constraints on the relative time delay of the image that arrived earlier.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 3 minor

Summary. The manuscript reports the discovery of SN 2022riv, a multiply imaged Type Ia supernova at z=1.522 in the lensing cluster RX J2129.7+0005, identified via HST SNAP observations and classified with JWST NIRSpec spectroscopy. The central result is a cosmology-independent magnification measurement of 5.35±1.01 for the last-to-arrive image, obtained by fitting its light curve with SALT3-NIR (and variants), with comparisons to six independent lens models and discussion of microlensing given the high stellar density environment near the BCG.

Significance. If the magnification measurement holds after addressing potential systematics, the result supplies a valuable independent anchor for cluster lens models and demonstrates the utility of JWST for time-domain lensing studies. The consistency across multiple SALT spectral templates and the explicit comparison to lens predictions (including nominal microlensing adjustments) are strengths, as is the placement in a high-magnification stellar-density regime that tests microlensing expectations.

major comments (2)
  1. [§3 (Light-curve analysis and SALT3-NIR fitting)] §3 (Light-curve analysis and SALT3-NIR fitting): The magnification 5.35±1.01 is derived under the assumption that the observed photometry is a constant scalar multiple of the standard Type Ia template. However, the location has stellar mass density 1-2 dex higher than SN Refsdal, with expected microlensing modulation of 20-50%. Time-varying microlensing (source motion across caustics or differential magnification across the photosphere) would distort light-curve shape parameters (stretch x1 and color c) recovered by SALT3-NIR in addition to amplitude, directly biasing the quoted value. The reported uncertainty (~19%) is comparable to the microlensing range, yet no time-dependent microlensing model or additional systematic term is included in the fit.
  2. [§4 (Lens model comparison)] §4 (Lens model comparison): Four models are stated to predict magnifications of 4-7 (within 1σ of the measurement) prior to microlensing, with a p<0.05 claim for greater precision than random. After nominal microlensing the HoliGRALE value (15.39±0.85) is brought into agreement. It is unclear how the nominal microlensing correction is computed or whether it accounts for shape distortions in the photometry rather than pure amplitude scaling; without this, the tension assessment and statistical claim on model precision are not fully supported.
minor comments (3)
  1. [Abstract and §2 (Observations)] The abstract and methods sections provide limited information on JWST NIRSpec data reduction, HST photometry extraction, and any pre-fitting corrections; explicit description of these steps (including any host subtraction or calibration) would allow better evaluation of photometric systematics.
  2. [§3 (Light-curve analysis)] The claim of consistency across multiple SALT SN spectral time-series models would be strengthened by reporting the specific models used, the range of recovered parameters (x0, x1, c), and quantitative measures of agreement (e.g., Δχ² or parameter covariance).
  3. [Figures and Tables] Figure captions and tables presenting the light-curve fits should explicitly note whether microlensing is assumed constant or time-varying, and include residual plots to illustrate any unmodeled structure.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments. We address each major point below and have revised the manuscript accordingly to strengthen the analysis and clarify the methods.

read point-by-point responses

  1. Referee: The magnification 5.35±1.01 is derived under the assumption that the observed photometry is a constant scalar multiple of the standard Type Ia template. However, the location has stellar mass density 1-2 dex higher than SN Refsdal, with expected microlensing modulation of 20-50%. Time-varying microlensing (source motion across caustics or differential magnification across the photosphere) would distort light-curve shape parameters (stretch x1 and color c) recovered by SALT3-NIR in addition to amplitude, directly biasing the quoted value. The reported uncertainty (~19%) is comparable to the microlensing range, yet no time-dependent microlensing model or additional systematic term is included in the fit.

    Authors: We agree that time-varying microlensing could in principle distort the recovered shape parameters x1 and c, introducing a bias beyond simple amplitude scaling. Our SALT3-NIR fits yield consistent magnification values across multiple independent spectral templates, which provides some empirical support for the robustness of the result. However, we acknowledge that no explicit time-dependent microlensing model was included. In the revised manuscript we have added an explicit discussion of this limitation in §3 and incorporated an additional systematic uncertainty of 0.4 mag (corresponding to ~20% in flux) into the final error budget to reflect the expected microlensing modulation range, increasing the total uncertainty to ±1.3. revision: yes

  2. Referee: Four models are stated to predict magnifications of 4-7 (within 1σ of the measurement) prior to microlensing, with a p<0.05 claim for greater precision than random. After nominal microlensing the HoliGRALE value (15.39±0.85) is brought into agreement. It is unclear how the nominal microlensing correction is computed or whether it accounts for shape distortions in the photometry rather than pure amplitude scaling; without this, the tension assessment and statistical claim on model precision are not fully supported.

    Authors: The nominal microlensing correction applied to the HoliGRALE prediction is a simple multiplicative scaling factor (median value ~0.4) drawn from the 20-50% modulation range expected at the high stellar-density location; this was intended as a first-order amplitude adjustment only. We recognize that the original text did not fully detail the computation or the statistical test underlying the p<0.05 claim. In the revised §4 we have expanded the description to specify the scaling method, to note that shape distortions are not modeled, and to provide the explicit procedure used for the precision test (comparison of model scatter against the measurement uncertainty after folding in the microlensing variance). These changes support the tension assessment while making the limitations transparent. revision: yes

Circularity Check

0 steps flagged

No significant circularity; magnification from external template fit

full rationale

The central result (magnification 5.35±1.01) is obtained by applying the standard SALT3-NIR fitter to observed JWST/HST photometry of the last image, using independent Type Ia spectral time-series templates. No paper-defined quantity is substituted for an input or output; the fit is a direct scaling of external models to data. Lens-model comparisons and microlensing discussion are post-hoc and do not enter the primary measurement. Multiple template variants are used only for robustness, not to define the result. The derivation chain is therefore self-contained against external benchmarks and does not reduce to self-definition, fitted-input renaming, or self-citation load-bearing.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard domain assumptions in supernova cosmology and gravitational lensing with no new free parameters, axioms, or invented entities introduced beyond the observational measurement itself.

axioms (2)
  • domain assumption Type Ia supernovae have sufficiently consistent intrinsic properties to allow light-curve fitting for magnification inference
    Invoked when applying SALT3-NIR to derive the magnification value
  • domain assumption The detected transient is strongly lensed by RX J2129.7+0005 producing multiple images
    Based on positional coincidence and cluster context

pith-pipeline@v0.9.0 · 5818 in / 1531 out tokens · 29620 ms · 2026-05-10T15:58:20.725830+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Strong Gravitational Lensing with the James Webb Space Telescope

    astro-ph.CO 2026-05 unverdicted novelty 2.0

    Strong gravitational lensing paired with JWST enables magnified high-resolution views of distant sources and improved constraints on dark matter.

Reference graph

Works this paper leans on

6 extracted references · 6 canonical work pages · cited by 1 Pith paper

  1. [1]

    2025, A&A , 699, A101, doi: 10.1051/0004-6361/202554468 Allingham, J

    Acebron, A., Bergamini, P., Rosati, P., et al. 2025, A&A , 699, A101, doi: 10.1051/0004-6361/202554468 Allingham, J. F. V., Zitrin, A., Kokorev, V., et al. 2026, arXiv e-prints, arXiv:2602.14074, doi: 10.48550/arXiv.2602.14074 Anderson, J. 2016, Empirical Models for the WFC3/IR PSF, Instrument Science Report WFC3 2016-12, 42 pages Anderson, J., & King, I....

    work page doi:10.1051/0004-6361/202554468 2025

  2. [2]

    Flattened G140M/100LP spectrum of SN 2022riv used for the SNID analysis (black line). The 23 best-matching SN Ib templates (green curves in the top panel) and 30 best-fitting SN Ic templates (blue curves in the bottom panel) with r × lap > 5 from SNID are shown for comparison. No SN II template matches were found. Arendse, N., M¨ ortsell, E., Weisenbach, ...

    work page doi:10.33232/001c.147126 2025

  3. [3]

    Catalog of multiple-image systems identified in the RX J2129 galaxy cluster field based on JWST/NIRCam obser- vations, including their corresponding spectroscopic redshifts. ID R.A. [deg.] Dec. [deg.] zspec 1a 322.4149230 0.0904156 0.6786 1b 322.4151893 0.0889741 0.6786 1c 322.4166530 0.0867530 0.6786 2a 322.4146395 0.0923864 0.9160 2b 322.4162941 0.08810...

    work page 2019

  4. [4]

    Same as in Table 11, but using the Salpeter IMF in the microlensing simulations and the HST WFC3/IR F110W band for synthetic photometry. Model Type Ia SN Explosion Model Double CO WD Merger N100 Sub-Chandrasekhar W7 µ Tension µ Tension µ Tension µ Tension GLAFIC 3.1+3.9 −1.4 0.6σ 3.1+4.5 −1.5 0.5σ 3.0+4.0 −1.4 0.6σ 3.1+4.3 −1.4 0.5σ Chen2020 4.3+10.2 −3.0...

    work page doi:10.1016/j.dark.2018.11.002 2018

  5. [5]

    Sys- tem 11 is well localized using JWST/NIRCam observations

    Cutout images showing prospective multiple- image candidates in the RX J2129 galaxy cluster field. Sys- tem 11 is well localized using JWST/NIRCam observations. Systems 10 and 12 are not clearly identifiable owing to their extended and complex morphologies. Dashed circles indicate the inferred positions of these systems. Bonvin, V., Tihhonova, O., Millon,...

    work page doi:10.1051/0004-6361/201833405 2019

  6. [6]

    11, but with synthetic photometric calculations performed using the HST WFC3/IR F110W band

    The same as in Fig. 11, but with synthetic photometric calculations performed using the HST WFC3/IR F110W band. 33 Foxley-Marrable, M., Collett, T. E., Vernardos, G., Goldstein, D. A., & Bacon, D. 2018, MNRAS , 478, 5081, doi: 10.1093/mnras/sty1346 Frye, B. L., Pascale, M., Pierel, J., et al. 2024, ApJ , 961, 171, doi: 10.3847/1538-4357/ad1034 Furtak, L. ...

    work page doi:10.1093/mnras/sty1346 2018