{"id":"b32b0d14-2eca-45d0-bd4f-7c20b3a446b7","arxiv_id":"2501.05513","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"AT 2023adsv is a likely Type IIP supernova at z=3.613, the most distant photometrically classified SN IIP with a spectroscopic host redshift.","lead":"JWST observations reveal a bright transient at redshift 3.6 that is most likely a Type II supernova, the most distant such object with a confirmed host redshift. The paper matches its light curve to an exploding 20-solar-mass red supergiant in a low-metallicity dwarf galaxy, offering a glimpse of how supernovae looked when the universe was under two billion years old.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The photometric Type II classification is not yet evidenced against the full model space: the PISN alternative explicitly fits, all MESA models fail late-epoch points, and F115W is excluded, so 'likely Type II' relies on a rate prior rather than on data.","rationale":"I read the paper in good faith. It is a careful, honest presentation of an interesting object: the host redshift is spectroscopically solid, the difference-imaging photometry is described in detail, and the text repeatedly flags the UV-template gap, the failed late-epoch model fits, and the PISN degeneracy. These strengths justify a conditional rather than a dismissive verdict. My concern overlaps with the reader's weakest assumption about template representativeness but is narrower and more load-bearing: the classification does not merely depend on the representativeness of the SN II template set; the paper's own evidence shows that the preferred model family fails part of the data and that a non-Type-II model (R175 PISN) matches the same photometry. The reduced chi-squared comparison in Table 3 is informative against Type Ia and Ib/c, but it is not a model posterior over the space of plausible high-z transients. With three epochs spanning only ~20 rest-frame days and no detectable SN spectral features, the phrase 'likely Type II' should be read as a rate-prior-weighted statement. The reader's CONDITIONAL verdict already captures this risk, so I do not recommend changing the verdict; I would only sharpen the condition: the classification should be presented as a candidate unless an expanded model comparison or a late-time observation breaks the PISN/IIn degeneracy.","tokens_in":22405,"tokens_out":7763,"duration_ms":81456,"concrete_test":"Re-run a single Bayesian model comparison on the Table 1 photometry over an expanded model set that includes (a) SN 2006kv plus UV extensions from the MESA/STELLA SEDs for F115W, (b) the R175 PISN model, (c) Type IIn/CSM models, and (d) a low-z UV-bright SN II template such as SN 2023ufx, with F115W included for all models. If the posterior weight of the SN II interpretation exceeds alternatives by a factor of at least 10 with a credible late-time prediction, the 'likely Type II' claim is supported; if PISN/IIn weights are comparable, the classification should be reported as a candidate with the event-rate prior made explicit. A single JWST NIRCam observation of the field roughly one to two years after discovery would also settle the issue: an SN IIP should fade by more than 3 magnitudes while a PISN should remain detectable.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is the photometric classification of AT 2023adsv as a likely Type II (SN IIP) at z=3.613. Three facts block this from being established by the light-curve fit alone. (1) The best-fit template SN 2006kv is fit without F115W, the only filter probing rest-frame ~2500 Å, so the blue UV flux that motivated the CSM and PISN discussion never enters the chi-squared comparison of Table 3. (2) In Section 3.3.1 the R175 PISN model 'matches well' and the authors state the dataset cannot differentiate PISN from RSG explosions; the preference for Type II is then a prior on event rates, not an inference from the photometry. (3) In Section 3.3 the MESA/STELLA models, including the preferred 20 Msun models, 'fail to fit the last epoch F200W, F277W, and F444W detections,' so the same observable that later epochs would use to separate SN II from PISN is not reproduced by any model. The reduced chi-squared values in Table 3 compare only a small template set (Ia, Ib/c, II) and do not include Type IIn, SLSN-I, or a range of PISN masses; with only three epochs and no SN spectral features, that comparison cannot support a posterior probability for 'likely Type II.' The paper's honest caveats save it from overclaiming, but the load-bearing part of the classification is an external rate argument, not a secure model fit.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the discovery and multi-band JWST light curve of AT 2023adsv, a transient at z=3.613 in a JADES field, and argues that it is a likely Type II supernova (specifically SN IIP-like), most distant of its kind with a spectroscopic redshift. The classification rests on a template fit (SN 2006kv, χ²/ν=1.10) that strongly disfavors SN Ia and SN Ib/c templates, plus MESA/STELLA light-curve models that favor a 20 Msun red supergiant progenitor with explosion energy 2×10^51 erg. The paper also derives host-galaxy properties (log M* ≈ 8.4, Z* ≈ 0.3 Zsun) and discusses the possibility of a pair-instability supernova (PISN), which it cannot rule out.","tokens_in":22736,"tokens_out":2534,"duration_ms":25285,"significance":"If the classification holds, this is a valuable probe of core-collapse supernovae in the early universe, with implications for progenitor masses, explosion energies, and the SN II rate at z>3. The paper is honest about its main limitations: no SN spectral features are isolated, F115W is excluded from the template fit, the PISN model matches the photometry, and all MESA models fail to reproduce the last-epoch detections in F200W, F277W, and F444W. These caveats are stated clearly, and the accompanying MESA/STELLA modeling and public data release are strengths. However, because the central 'likely Type II' claim depends on a prior on PISN rates rather than on a secure fit, the paper's significance is conditional on further observations or a more complete model comparison.","major_comments":[{"comment":"The template-fit χ²/ν comparison that drives the Type II classification is performed without F115W, the only filter probing rest-frame ~2500 Å at z=3.613. The paper states that no template covers this wavelength and therefore excludes it from the fit (§3.1). Yet the early blue UV flux seen in F115W and F150W is precisely the feature that motivates the confined-CSM and PISN alternatives in §3.3. The classification not only leaves out a discriminating band, but excludes the band where the empirical templates are most likely to be unrepresentative. Please quantify the effect of including F115W (for example, by using UV-extended templates or by showing the predicted F115W flux of SN 2006kv and the resulting change in Δχ²) or otherwise justify that the exclusion does not bias the Type II preference.","section":"§3.1, Table 3"},{"comment":"The paper states that the 175 Msun PISN model 'matches well' to the photometry and that 'the dataset as it stands is not sufficient to differentiate between a PISN model and those explored' in §3.3. The conclusion that AT 2023adsv is 'likely to be a RSG explosion' is then justified by 'the expected low PISN event rates.' This is a prior, not an inference from the photometric data. The central claim 'likely Type II' therefore rests on an external rate argument. To make the claim quantitative, please present a formal comparison, e.g., the Δχ² between the best RSG model and the PISN model on the same photometric points, or a posterior probability that includes an explicit rate prior. As written, the abstract and conclusions overstate the evidential weight of the light curve alone.","section":"§3.3.1"},{"comment":"Section 3.3 states that 'all models fail to fit the last epoch F200W, F277W, and F444W detections,' which are the same bands that would discriminate between SN II and PISN at late times. Despite this, the section concludes that the best overall fit is the 20 Msun progenitor. This conclusion is not supported by any reported fit statistic for the MESA/STELLA models (Table 3 lists only the empirical template fits; the model fits in Figure 6 are presented visually). Please report reduced χ² or equivalent goodness-of-fit values for the RSG models (with and without CSM) and for the PISN model, computed over all filters and epochs, so that the 'best overall fit' claim can be evaluated. Without such statistics, the preferred-progenitor inference is not quantitatively grounded.","section":"§3.3, §3.4"}],"minor_comments":[{"comment":"The reference list contains duplicate entries: Kasen et al. (2011) appears twice, and Pierel et al. (2024a,b,c) each appear twice with identical bibliographic data. Please consolidate the list and renumber citations consistently.","section":"References"},{"comment":"The text mentions 'SN 20015bs' in the Introduction; this is presumably a typo for SN 2015bs (or another object). Please verify the object name and year.","section":"§1"},{"comment":"In the sentence describing the horizontal dashed lines in Figure 5, 'the the 1.0, 0.3, and 0.1 solar oxygen abundance values' contains a duplicated article. Please fix this and similar typographical issues in the figure captions.","section":"§3.2"},{"comment":"The Conclusion contains 'we limited our our analysis' — the duplicated 'our' should be removed. Also, the companion paper Moriya et al. (2025) is cited as arXiv:2501.xxxxx; this placeholder needs to be replaced with the actual identifier before publication.","section":"§5"},{"comment":"The legend labels 'T ype II', 'T ype Ib/c', and 'T ype Ia' contain a spurious space after the capital T. Please correct the label formatting.","section":"Figure 3"}],"recommendation":"major_revision","confidential_remarks":"The paper's central claim is reasonable as a 'likely' classification, but the quantitative support is weakened by the exclusion of F115W from the template fit and by the admitted inability to rule out PISN. The manuscript would be strengthened by adding fit statistics for the MESA/STELLA and PISN models and by framing the Type II preference as prior-dependent. The paper is within scope for an astrophysics journal and the data release is a positive feature."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this is a solid single-object discovery paper with an unusually honest limitations section. The new result is a likely SN IIP at z=3.613 with a spectroscopic host redshift, the most distant such object yet published. The photometry is carefully reduced with difference imaging and PSF fitting, and the host redshift and metallicity work is thorough. Credit where due: the paper explicitly tells you that F115W is excluded from the template fit, that the PISN model matches well, and that all MESA/STELLA models fail the last-epoch detections in F200W, F277W, and F444W. That level of candor makes the 'likely' in the title earned.\n\nThe soft spot is the classification itself. With three epochs, no SN spectral features, and only a small template set, the chi-squared comparison (II at 1.10 vs Ib/c at 6.76 and Ia at 16.63) is suggestive but not conclusive. The paper's own modeling admits the PISN alternative cannot be ruled out and that the preference for Type II rests on the low expected PISN rate. That is a rate prior, not a photometric discriminant. The F115W exclusion matters because the blue UV flux is exactly where CSM interaction and PISN models would differ from a plain RSG explosion. And the last-epoch model failures mean the late-time behavior that would separate these scenarios is not reproduced by any of the preferred models. None of this invalidates the discovery, but it does mean the Type II classification is provisional in a way that the chi-squared table alone doesn't convey.\n\nThe host metallicity inference also has a tension worth noting: Prospector gives about 0.02 Zsun while the O3O2 line ratio gives 0.3 Zsun. The authors adopt the latter with reasonable justification, but the factor-of-ten spread is larger than the quoted uncertainty. The progenitor mass and explosion energy claims inherit that uncertainty.\n\nWho is this for? Anyone working on high-z transients or JWST time-domain science. It is a well-documented, record-breaking candidate that will be a reference point for future samples. It deserves serious peer review. My recommendation: send it to referees. The classification and the modeling caveats should get close scrutiny, but the paper's transparency makes that scrutiny productive.","headline":"A careful, honest single-object paper reporting a record-breaking SN IIP candidate at z=3.6; the classification is provisional because the data cannot exclude a PISN, but the paper earns its place through transparency.","tokens_in":23470,"tokens_out":2678,"would_cite":true,"duration_ms":23200,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"JWST data identify AT 2023adsv as a likely Type IIP supernova at z=3.6, the most distant one with a spectroscopic redshift.","keywords":["supernovae","Type IIP supernovae","high-redshift transients","JWST","core-collapse supernovae","low-metallicity galaxies","light curve classification","pair-instability supernovae"],"falsifier":"A NIRSpec spectrum taken during the hydrogen-recombination plateau that shows broad $\\mathrm{H}\\alpha$ or Fe II $\\lambda 5018$ absorption would confirm the Type II identification; a spectrum with no hydrogen features, or photometry that keeps rising instead of entering a plateau, would rule it out. A later JWST epoch that shows the source still bright hundreds of rest-frame days after peak would favor the $175\\,M_\\odot$ pair-instability alternative over the inferred red supergiant explosion.","tokens_in":22213,"feed_emoji":"💥","tokens_out":14540,"duration_ms":128038,"temperature":0.7,"pith_summary":"This paper reports the discovery and classification of AT 2023adsv, a transient caught in JWST deep images of a galaxy at spectroscopic redshift $z = 3.613 \\pm 0.001$. The authors argue that its multi-band light curve is best matched by a normal Type IIP supernova template with a peak absolute magnitude $M_B \\approx -18.3$ mag, making it the most distant photometrically classified Type IIP supernova with a measured redshift. Synthetic explosion models favor a roughly $20\\,M_\\odot$ red supergiant progenitor with an explosion energy of about $2 \\times 10^{51}$ erg, higher than typical for local Type IIP supernovae but consistent with low-metallicity progenitors. If the classification holds, the object opens a window onto core-collapse supernovae when the Universe was less than two billion years old and suggests that Type IIP supernovae may be systematically brighter at low metallicity.","feed_headline":"Most distant Type IIP supernova candidate found at z=3.6","feed_subtitle":"JWST data favor a 20-solar-mass progenitor and an unusually energetic explosion in a low-metallicity galaxy.","key_machinery":"The argument is carried by light-curve template matching backed by synthetic explosion models. Observed spectral templates of supernova subtypes are redshifted and fitted to the photometry in the observer-frame JWST filters, with the best-fitting template determining both the type and the peak luminosity. A grid of red supergiant progenitor models with masses of 12, 16, and 20 solar masses at 0.3 solar metallicity, with and without a confined circumstellar shell, is evolved and exploded with varied energies to predict light curves; the 20 solar mass models with roughly $2\\times10^{51}$ erg match best. Host metallicity is pinned by the O3O2 ratio (the [O III]/[O II] line ratio) of the forbidden oxygen lines in the NIRSpec spectrum, because the supernova's own spectral features are too contaminated by host light to measure directly.","core_discovery":"The central claim is that AT 2023adsv is a Type II supernova, specifically a Type IIP, defined as a hydrogen-rich core-collapse explosion whose light curve lingers on a plateau. The classification is photometric: the six-filter JWST light curve is fitted against empirical spectral templates, and the normal Type IIP template SN 2006kv wins with reduced $\\chi^2/\\nu = 1.10$, while Type Ia and Type Ib/c templates are strongly disfavored ($16.63$ and $6.76$). Matching that template to the observed brightness puts the peak at $M_B = -18.3 \\pm 0.1$ mag, about $0.5$ mag brighter than SN 2006kv itself but still within the local Type II luminosity range. Synthetic light curves from red supergiant progenitors at $0.3\\,Z_\\odot$ favor a $20\\,M_\\odot$ zero-age main-sequence star exploding with about $2\\times 10^{51}$ erg, and the authors explicitly note that a $175\\,M_\\odot$ pair-instability model also fits well enough that the current data cannot exclude it. They conclude that AT 2023adsv is the most distant photometrically classified Type IIP supernova with a spectroscopic redshift and may represent a redshift-dependent shift in Type IIP properties.","pith_inferences":["The authors leave implicit that the one filter excluded from the template fit probes rest-frame $\\sim2500$ Å, exactly where low-metallicity line blanketing is expected to weaken; future samples could turn that same excess into a photometric metallicity proxy for high-redshift Type II supernovae.","Because every explosion model fails to reproduce the last epoch's F200W, F277W, and F444W detections, a single additional JWST epoch at matched depth would sharpen the choice between a fading Type IIP, late circumstellar interaction, and a pair-instability explosion.","A post-fade NIRSpec observation of the same host, taken with the same shutters, would let the host serve as its own template and could reveal whether broad supernova features were hidden beneath the host light in the existing spectrum.","The roughly $0.5$ mag overluminosity relative to SN 2006kv is attributed to higher explosion energy, but the degeneracy between progenitor radius, circumstellar material, and metallicity means one object cannot separate these; a survey sample would be required to establish a true redshift trend."],"forward_implications":["AT 2023adsv becomes the most distant photometrically classified Type IIP supernova with a spectroscopic redshift, pushing the empirical baseline for core-collapse supernovae from $z\\approx2.5$ out to $z=3.6$.","The favored explosion model implies a roughly $20\\,M_\\odot$ red supergiant progenitor and an explosion energy near $2\\times10^{51}$ erg, higher than typical local Type IIP energies.","The host's low mass and low metallicity ($Z_* \\approx 0.3\\,Z_\\odot$) fit the high-redshift mass-metallicity relation, making the object a test of whether low-metallicity Type IIP supernovae are brighter and bluer.","The current data cannot distinguish a normal red supergiant explosion from a $175\\,M_\\odot$ pair-instability supernova, so continued monitoring of this source is required.","If representative, JWST-era samples of high-redshift Type IIP supernovae could become probes of metallicity and massive-star populations in the first two billion years of cosmic history."],"supporting_citations":[{"why":"Defines the deep JWST transient search that discovered AT 2023adsv and gives the survey context.","marker":"D24"},{"why":"Provides the SN 2006kv spectral template that yields the best Type IIP light-curve match.","marker":"D'Andrea et al. 2010"},{"why":"Supplies the library of core-collapse supernova spectral templates used in the subtype comparison.","marker":"Pierel et al. 2018"},{"why":"Supplies the SALT3-NIR Type Ia light-curve model used as the strongly disfavored Type Ia comparison.","marker":"Pierel et al. 2022"},{"why":"Provides the red supergiant progenitor structures and synthetic light curves used to infer the 20 solar mass, high-energy explosion.","marker":"Moriya et al. 2025"},{"why":"Provides the 175 solar mass pair-instability supernova model that also fits and cannot be excluded.","marker":"Kasen et al. 2011"},{"why":"Provides the O3O2 oxygen-line diagnostic used to derive the host gas-phase metallicity.","marker":"Curti et al. 2020"},{"why":"Supplies the local low-metallicity Type IIP comparison sample used in the plateau-luminosity versus host-luminosity analysis.","marker":"Scott et al. 2019"},{"why":"Gives the local Type II absolute magnitude distribution used to place the bright peak within the normal range.","marker":"Richardson et al. 2014"}],"fun_headline_variants":["JWST spots likely Type IIP supernova at z=3.6","Most distant Type IIP supernova candidate found at z=3.6","Supernova at z=3.6 from 20-solar-mass star, likely Type IIP","Likely Type IIP supernova at z=3.6 sets distance record","Supernova at z=3.6: likely Type IIP, most distant yet"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The classification assumes that local Type IIP templates and the three red supergiant model families adequately represent what a low-metallicity supernova at $z=3.6$ looks like, even though the shortest-wavelength measurement had to be excluded from the template fit and none of the models reproduce the last epoch's redder detections.","fun_headline_variants_meta":{"raw":{"variants":["JWST spots likely Type IIP supernova at z=3.6","Most distant Type IIP supernova candidate found at z=3.6","Supernova at z=3.6 from 20-solar-mass star, likely Type IIP","Likely Type IIP supernova at z=3.6 sets distance record","Supernova at z=3.6: likely Type IIP, most distant yet"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001234,"raw_usage":{"total_tokens":5181,"prompt_tokens":1174,"completion_tokens":4007,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":790,"completion_tokens_details":{"reasoning_tokens":3898}},"tokens_in":790,"tokens_out":4007,"duration_ms":28113,"temperature":1.0,"reasoning_tokens":3898,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:12:54.245316+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A NIRSpec spectrum taken during the hydrogen-recombination plateau that shows broad $\\mathrm{H}\\alpha$ or Fe II $\\lambda 5018$ absorption would confirm the Type II identification; a spectrum with no hydrogen features, or photometry that keeps rising instead of entering a plateau, would rule it out. A later JWST epoch that shows the source still bright hundreds of rest-frame days after peak would favor the $175\\,M_\\odot$ pair-instability alternative over the inferred red supergiant explosion.","supporting_citations":[{"cited_title":"J., Coulter, D","cited_arxiv_id":null,"evidence_quote":"Provides the red supergiant progenitor structures and synthetic light curves used to infer the 20 solar mass, high-energy explosion."}],"review_version":1}