{"id":"72eedf2d-0099-4cf3-8c81-35a54a3ea554","arxiv_id":"1908.07807","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"SN 2018hna is a 1987A-like Type II supernova whose early light curves show the cooling emission after shock breakout, indicating a compact blue supergiant progenitor about 50 solar radii across.","lead":"Astronomers tracked a newly found stellar explosion, SN 2018hna, and show it belongs to the rare 1987A-like class of supernovae, which explode from compact blue supergiant stars rather than the usual red giants. It is one of only a couple of such events caught early enough to see the cooling glow left right after the shock wave broke out of the star.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The explosion epoch and the no-CSM assumption rest on one STELLA fit with no early-time spectra; this weakens the shock-breakout timing and the compact-progenitor parameters, although the 1987A-like classification has independent support.","rationale":"The reader's weakest_assumption identifies the fitted explosion epoch and the assumed absence of CSM interaction as the most load-bearing point. I agree: the title's shock-breakout signature and the derived progenitor radius, mass, and energy all depend on the early-time model fit, while the no-CSM argument rests on spectra that begin only at about +12 days, after most of the cooling phase. The additional discrepancy between the STELLA and Arnett parameter estimates in Section 5.1 reinforces that the quoted ranges are systematic envelopes rather than a single consistent solution. However, the later-phase evidence for a 1987A-like classification is strong and largely independent of the exact explosion epoch: slow rise observed from discovery, Ba II features, velocity evolution, color evolution, and nebular-phase line profiles. The paper therefore merits a conditional acceptance with the quantitative early-time claims flagged as model-dependent, which is exactly the reader's verdict. No change to the reader's recommendation is needed.","tokens_in":12188,"tokens_out":9277,"duration_ms":97080,"concrete_test":"Re-fit the first about 14 days of Swift uvw1, U, B, V, and R photometry with an independent model, such as the Nakar & Piro (2014) cooling-envelope model or a small STELLA grid, treating t_explosion, progenitor radius, energy-to-mass ratio, and a CSM luminosity term as free parameters, and compute confidence contours. If the best-fit epoch shifts by more than about 5 days, or if a progenitor radius above 100 R_sun is within the 1-sigma contour, then the reported 88 day rise time and the compact blue-supergiant radius should be presented as model-dependent rather than robust measurements.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section 3 sets the explosion epoch to JD 2458411.3 solely from a STELLA fit to the first Swift points; the same fit is used in Section 5.1 to infer a radius of about 50 R_sun, a pre-SN mass of about 16 M_sun, and an explosion energy of about 1.7e51 erg. Every phase-dependent claim, including the 88 day V-band rise time, the 14 day cooling phase, and the velocity epochs, is measured from this fitted epoch. No confidence interval is reported for the epoch, and the adopted no-CSM assumption is checked only against spectra starting at about +12 d (Section 5.1), after most of the cooling emission has already occurred. A moderate CSM contribution or a 3-5 day epoch shift would change the rise time and the inferred progenitor parameters. In addition, the Section 5.1 Arnett scaling estimate (ejecta mass about 19.8 M_sun, energy about 2.9e51 erg) does not agree with the STELLA solution (ejecta mass about 14 M_sun, energy about 1.7e51 erg), so the quoted mass and energy ranges are not a consistent confidence interval. The 1987A-like classification itself is supported by later-phase observables such as Ba II features, color evolution, velocity curves, and nebular lines, so the concern mainly affects the shock-breakout timing and the quantitative progenitor claims rather than the classification as a 1987A-like event.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents high-cadence UV, optical, and NIR photometry and low-resolution optical spectroscopy of SN 2018hna from shortly after discovery to ~256 days. The authors identify an early (<14 day) multi-band decline that they attribute to adiabatic cooling of shock-heated ejecta following shock breakout, and a V-band rise time of ~88 days, similar to SN 1987A. Hydrodynamic modeling with STELLA of the early light curves yields an explosion epoch JD 2458411.3, a pre-SN mass of ~16 M_sun, radius ~50 R_sun, and explosion energy ~1.7e51 erg; an Arnett-scaling estimate gives ejecta mass ~19.8 M_sun and energy ~2.9e51 erg. From the bolometric light curve they infer a 56Ni mass of ~0.087 +/- 0.004 M_sun. The paper concludes that SN 2018hna is a 1987A-like event, only the second BSG explosion caught within days of shock breakout, and that its host UGC 07534 has sub-solar metallicity.","tokens_in":12425,"tokens_out":3919,"duration_ms":41277,"significance":"If the central claims hold, this paper substantially enlarges the small sample of 1987A-like supernovae with early-time multi-band coverage, and the shock-cooling detection would provide a direct constraint on a blue supergiant progenitor. The classification as 1987A-like rests on several mutually independent later-phase observables: the slow ~88 day rise, early Ba II features, color evolution, line velocities, and nebular-phase line profiles. The dataset is rich (Swift UVOT plus ground-based optical/NIR and a long spectral sequence), and the STELLA modeling is a reasonable first step. However, the quantitative progenitor parameters and the shock-breakout timing depend on a single model fit whose uncertainty is not characterized, and the two parameter estimates quoted in the abstract are not mutually consistent. These issues must be addressed before the quantitative claims can be accepted.","major_comments":[{"comment":"The explosion epoch JD 2458411.3 is derived solely from the STELLA fit to the early Swift light curves, and no uncertainty or independent estimate is given. Every phase-dependent quantity in the paper, including the ~88 day V-band rise time, the ~14 day cooling phase, and the velocity epochs in Fig. 3, is measured relative to this fitted epoch. Please report the epoch uncertainty and provide a robustness test that varies the epoch by at least ±2–3 days; if any pre-discovery nondetections exist, use them to bracket the epoch independently.","section":"§3 and §5.1"},{"comment":"The two quoted progenitor parameter estimates are not consistent with each other: the STELLA fit gives an ejecta mass of ~14 M_sun and an explosion energy of ~1.7e51 erg, while the Arnett scaling gives ~19.8 M_sun and ~2.9e51 erg. The abstract and §6 quote mass and energy ranges of 14–20 M_sun and 1.7–2.9e51 erg as though they were a single confidence interval, but these are two different estimates with different systematic assumptions. Please discuss the origin of the discrepancy, propagate uncertainties from distance, reddening, and nickel mass in a consistent way, and quote the parameters from either a single method or a properly constructed systematic error budget.","section":"§5.1"},{"comment":"The assumption of no circumstellar-medium interaction is justified only by the absence of spectral interaction features, but the first spectrum is at ~12 days after the fitted explosion epoch, which is after most of the claimed cooling emission (0–14 days) has passed. A moderate CSM component could affect the early light-curve shape and hence the fitted epoch, radius, and energy, without producing detectable narrow lines at +12 days. Please quantify this degeneracy, for example by running STELLA models with a small CSM mass or by using early-time luminosity/color limits to constrain any CSM contribution.","section":"§5.1"},{"comment":"The quoted 56Ni mass uncertainty of ±0.004 M_sun appears inconsistent with the stated distance modulus uncertainty of ±0.29 mag. A 0.29 mag uncertainty alone corresponds to roughly 15% in luminosity, which would translate to at least ±0.012 M_sun in the derived nickel mass before any other error sources are included. Please propagate the full error budget (distance, reddening, SED integration, flux calibration) and either revise the quoted uncertainty or explain why the nickel mass is insensitive to these terms.","section":"§5.2"}],"minor_comments":[{"comment":"The phrase \"Wein's part of the spectrum\" should read \"Wien part of the spectrum\".","section":"§5.1"},{"comment":"The claim that SN 2018hna is \"only the second BSG event caught within a few days from shock breakout\" should be reconciled with the introduction, which lists SNLS-04D2dc and SN 2010aq as displaying cooling emission from shock breakout; please clarify whether these events are excluded because their progenitors were not confirmed as BSGs or for another reason.","section":"§6 and §1"},{"comment":"The SN 1987A light curves are plotted as \"1987A + Const.\", but the constant shifts are not specified; adding the shifts in the caption or plotting the overlaid curves in a separate panel would make the comparison reproducible.","section":"Figure 1"},{"comment":"The unidentified feature at ~8360 Å in the nebular spectrum is noted as warranting further investigation; adding a brief comparison to similar unidentified features in other Type II SNe would be useful.","section":"Figure 2D"}],"recommendation":"major_revision","confidential_remarks":"The later-time evidence for the 1987A-like classification is strong and independent of the STELLA fit, so I do not see a basis for rejection. However, the early-time shock-breakout claim and the quantitative progenitor parameters rest on a single model fit with no reported uncertainty, and the two parameter estimates are not consistent. In a Letter format, the authors may need to either add the requested robustness checks or moderate the quantitative claims. Please also verify the novelty claim that this is \"only the second BSG event caught within a few days from shock breakout,\" since SNLS-04D2dc and SN 2010aq are cited in the introduction as showing cooling emission."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Hi [Name],\n\nThe paper is a solid observational Letter on SN 2018hna, a new member of the small 1987A-like class. The main value is the data: Swift began within about three days of explosion, which is rare for these events, and the follow-up spans photometry and spectroscopy out to ~256 days. The classification is robust. The slow ~88 day V-band rise, Ba II features, early color evolution, and velocity profiles all point to a compact BSG progenitor. That part holds together.\n\nThe paper's quantitative claims are weaker. The explosion epoch (JD 2458411.3) is not measured; it is a free parameter in the STELLA fit to the early Swift light curves. Every phase-dependent statement, the rise time, the 14 day cooling phase, the velocity epochs, uses that fitted epoch, and no confidence interval is given for it. The no-CSM assumption is checked only with spectra starting at +12 d, after most of the cooling emission is over. A few-day epoch error or a modest CSM contribution would change the rise time and the inferred radius, mass, and energy. This is the main soft spot, and it is not minor.\n\nSecond, the quoted ranges for ejecta mass (14–20 Msun) and explosion energy (1.7–2.9e51 erg) combine two estimates that do not agree with each other: the STELLA fit gives ~14 Msun and ~1.7e51, while the Arnett scaling gives ~19.8 Msun and ~2.9e51. Presenting them as a single range hides the discrepancy. The difference is probably systematic, but the paper does not reconcile it.\n\nThird, the 56Ni mass uncertainty of ±0.004 Msun is only the statistical error. The distance modulus has ±0.29 mag, which yields roughly a 30% luminosity uncertainty, so the systematic error on the nickel mass is much larger than the quoted error. This should be stated.\n\nMinor point: the title says 'signature of shock breakout.' The data show the post-breakout cooling emission, not the breakout flash itself. That is a defensible phrasing, but a little generous.\n\nWho benefits: this is for SN observers and modelers working on the 1987A-like subclass. It adds a data point to a sample of only about ten events, and the early coverage is genuinely useful. The paper deserves refereeing; it is not a desk reject. A referee should push for a quantitative treatment of the epoch uncertainty, a reconciliation (or at least an acknowledgment) of the two mass/energy estimates, and a realistic error budget for the nickel mass.\n\nI'd send it out.","headline":"A useful new 1987A-like SN with rare early data; the classification holds, but the explosion epoch and progenitor parameters carry model-dependent uncertainties that the paper understates.","tokens_in":13205,"tokens_out":3222,"would_cite":true,"duration_ms":31735,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"SN 2018hna is a 1987A-like Type II supernova whose early light curves carry the cooling signature of a shock breakout from a compact blue supergiant.","keywords":["Type II supernova","SN 1987A-like","shock breakout","blue supergiant progenitor","cooling envelope emission","radiation-hydrodynamics modeling","supernova light curves","UGC 07534"],"falsifier":"Catch the next 1987A-like event with a high-cadence UV survey that records the actual shock-breakout flash and compare that independently measured explosion date with the date obtained by fitting the post-breakout cooling model; a mismatch of more than a few days, or detection of narrow emission lines or radio/X-ray excess from circumstellar interaction within the first two weeks, would overturn the derived rise time and progenitor parameters.","tokens_in":11908,"feed_emoji":"💥","tokens_out":11824,"duration_ms":163400,"temperature":0.7,"pith_summary":"The paper identifies SN 2018hna as a member of the rare 1987A-like class of Type II supernovae. Its ultraviolet, optical, and near-infrared light curves decline for roughly the first 14 days, which the paper reads as adiabatic cooling of shock-heated ejecta following shock breakout, and then rise slowly to a V-band maximum at about 88 days, matching SN 1987A. Hydrodynamic modeling of the cooling phase with the STELLA code points to a compact blue supergiant progenitor with radius around 50 $R_\\odot$, mass 14–20 $M_\\odot$, and explosion energy 1.7–2.9 $\\times 10^{51}$ erg. The paper also infers a $^{56}$Ni mass of about 0.087 $M_\\odot$ and a sub-solar host metallicity (about 0.3 $Z_\\odot$). If correct, SN 2018hna becomes only the second blue-supergiant explosion caught within a few days of shock breakout, showing that early multi-band photometry can directly probe the progenitor.","feed_headline":"Second blue-supergiant supernova caught days after shock breakout","feed_subtitle":"Early light curves show shock-cooled ejecta, an 88-day rise, and a compact 50-solar-radius progenitor.","key_machinery":"The load-bearing machinery is the STELLA multigroup radiation-hydrodynamics code, which simulates the explosion of a compact blue supergiant and computes multicolor light curves by convolving the synthetic spectral energy distribution with filter transmission functions; the early Swift photometry is then matched to these models, fixing the explosion epoch and giving the progenitor radius, mass, and explosion energy. The observational counterpart is the cooling envelope emission itself: the early decline in the UV and optical bands followed by a rise in redder bands as the photosphere recombines around 6000–8000 K, whose luminosity and timescale depend on the progenitor radius and the ejecta energy-to-mass ratio. A secondary mechanism, the Arnett diffusion-time relation calibrated to SN 1987A, supplies the higher end of the inferred mass and energy.","core_discovery":"The central discovery is that SN 2018hna was caught close enough to its explosion to show the shock-breakout cooling: the Swift UVOT light curves decline for about 14 days from an explosion epoch of JD 2458411.3, while the optical bands initially rise and then settle, the behavior expected when a compact, shock-heated envelope expands and recombines. Fitting STELLA multigroup radiation-hydrodynamic models to those cooling light curves yields a pre-SN mass near 16 $M_\\odot$ (ejecta mass near 14 $M_\\odot$), a radius near 50 $R_\\odot$, and an explosion energy near 1.7 $\\times 10^{51}$ erg; scaling by the Arnett diffusion relation gives about 19.8 $M_\\odot$ and 2.9 $\\times 10^{51}$ erg, hence the quoted ranges 14–20 $M_\\odot$ and 1.7–2.9 $\\times 10^{51}$ erg. With a V-band rise time of about 87.5 days, a peak absolute magnitude of $-16.35 \\pm 0.32$, and a $^{56}$Ni mass of $0.087 \\pm 0.004\\,M_\\odot$, the event aligns with SN 1987A and the 1987A-like class, and no spectral feature indicates circumstellar interaction. Its host, UGC 07534, is a low-luminosity dwarf irregular with sub-solar metallicity of about 0.3 $Z_\\odot$, consistent with the environments of other 1987A-like events.","pith_inferences":["If the paper's interpretation is correct, current surveys without rapid UV response are likely missing the shock-breakout-cooling phase in most 1987A-like events, and a dedicated high-cadence UV survey should reveal that this phase is common among compact-progenitor Type II supernovae.","The high ratio of peak luminosity to radioactive-decay luminosity (about 2.5, versus about 1.5 in SN 1987A) hints at a different $^{56}$Ni distribution or mixing, which a systematic comparison across the class could test against mixing prescriptions.","The transient flux excesses (\"kinks\") in the H$\\alpha$ and Na I D troughs, attributed to asymmetry in the ejecta, could be tested directly with spectropolarimetry of a future 1987A-like event.","The early CO emission at about 153 days, taken as evidence of dust formation, suggests that compact-progenitor explosions may form dust earlier than red supergiant explosions; a larger sample with near-infrared spectroscopy could test whether progenitor compactness controls the timing of dust onset."],"forward_implications":["SN 2018hna becomes the second blue-supergiant supernova caught within a few days of shock breakout, so early Swift-like multi-band photometry can identify the 1987A-like class from cooling envelope emission alone.","The inferred compact progenitor and high explosion energy support the theoretical idea that blue supergiants can explode as Type II supernovae through fast rotation, low metallicity, or binary interaction.","The sub-solar host metallicity (about 0.3 $Z_\\odot$) reinforces the pattern that 1987A-like events occur in late-type, low-metallicity galaxies.","The roughly 88-day V-band rise time and early Ba II features give practical photometric and spectroscopic discriminators between 1987A-like and normal Type II supernovae.","The similarity of the cooling emission's luminosity and timescale to SN 1987A implies a progenitor radius and an ejecta energy-to-mass ratio close to those of SN 1987A."],"supporting_citations":[{"why":"Supplies the STELLA code whose synthetic multicolor light curves are fitted to the early cooling phase to fix the explosion epoch and infer progenitor properties.","marker":"Blinnikov et al. 2000"},{"why":"Gives the physical scaling of post-shock-breakout cooling emission with progenitor radius and ejecta energy-to-mass ratio used to interpret the early light curves.","marker":"Nakar & Piro 2014"},{"why":"Models the shock-breakout cooling emission and documents the same early decline seen in SN 1987A, the comparison template.","marker":"Ensman & Burrows 1992"},{"why":"Supplies the diffusion-time relation used to scale from SN 1987A and estimate the ejecta mass and explosion energy.","marker":"Arnett 1979"},{"why":"Establishes the slow rise to maximum as the distinguishing photometric feature of 1987A-like supernovae and supplies comparison objects.","marker":"Kleiser et al. 2011"},{"why":"Compiles the properties of 1987A-like events, including the trend that bluer colors correspond to brighter maxima and higher synthesized nickel-56.","marker":"Taddia et al. 2016"},{"why":"Provides the sample of 1987A-like events and the claim that they arise from compact progenitors with high explosion energy and nickel-56 mass.","marker":"Pastorello et al. 2012"},{"why":"Explains the early strong Ba II features in SN 1987A as a consequence of faster cooling from a compact progenitor, the basis for using Ba II as a diagnostic.","marker":"Mazzali & Chugai 1995"},{"why":"Provides the luminosity-metallicity relation from which the sub-solar host metallicity of about 0.3 Zsun is derived.","marker":"Tremonti et al. 2004"}],"fun_headline_variants":["Second 1987A-like supernova spotted with shock-breakout signature","Shock-breakout cooling caught in rare 1987A-like supernova","Early shock-cooling reveals second 1987A-like supernova","Only second 1987A-like SN caught with shock-breakout signature","Shock breakout captured in 1987A-like supernova, only second"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"Everything rests on the assumed explosion epoch, which is not directly observed but fixed by fitting the STELLA cooling model to the first photometric points; if that fit is off by a few days or if early circumstellar interaction contributed to the light, the rise time, inferred radius, mass, and energy would all shift.","fun_headline_variants_meta":{"raw":{"variants":["Second 1987A-like supernova spotted with shock-breakout signature","Shock-breakout cooling caught in rare 1987A-like supernova","Early shock-cooling reveals second 1987A-like supernova","Only second 1987A-like SN caught with shock-breakout signature","Shock breakout captured in 1987A-like supernova, only second"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000977,"raw_usage":{"total_tokens":4247,"prompt_tokens":1137,"completion_tokens":3110,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":753,"completion_tokens_details":{"reasoning_tokens":3010}},"tokens_in":753,"tokens_out":3110,"duration_ms":536849,"temperature":1.0,"reasoning_tokens":3010,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T11:57:14.520725+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Catch the next 1987A-like event with a high-cadence UV survey that records the actual shock-breakout flash and compare that independently measured explosion date with the date obtained by fitting the post-breakout cooling model; a mismatch of more than a few days, or detection of narrow emission lines or radio/X-ray excess from circumstellar interaction within the first two weeks, would overturn the derived rise time and progenitor parameters.","supporting_citations":[{"cited_title":"1992, ApJ, 393, 742","cited_arxiv_id":null,"evidence_quote":"Models the shock-breakout cooling emission and documents the same early decline seen in SN 1987A, the comparison template."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the diffusion-time relation used to scale from SN 1987A and estimate the ejecta mass and explosion energy."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the slow rise to maximum as the distinguishing photometric feature of 1987A-like supernovae and supplies comparison objects."},{"cited_title":"2016, A&A, 588, A5 Tak´ ats, K., Pignata, G., Bersten, M., et al","cited_arxiv_id":null,"evidence_quote":"Compiles the properties of 1987A-like events, including the trend that bluer colors correspond to brighter maxima and higher synthesized nickel-56."},{"cited_title":"A., & Chugai, N","cited_arxiv_id":null,"evidence_quote":"Explains the early strong Ba II features in SN 1987A as a consequence of faster cooling from a compact progenitor, the basis for using Ba II as a diagnostic."}],"review_version":1}