{"id":"e7704360-e25a-41be-81ea-eac70f8582e6","arxiv_id":"2507.06391","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Binary mass accretors and stellar mergers produce hydrogen-rich Type II supernovae whose explosion energies, nickel masses, and neutron star masses are set by the pre-collapse core entropy, not by the binary history.","lead":"This paper models how stars that gain mass from a binary companion or merge with one explode as supernovae, computing explosion energies, nickel yields, and neutron star masses for hundreds of progenitor models. It finds that these explosion properties depend mainly on the core structure at collapse, not on the star's binary history, and uses this to explain long-lasting Type IIP supernovae and some exotic interacting supernovae.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The history-independence claim is only tested for thermal-timescale accretion on non-rotating, unmixed single-star models; true merger physics (mixing, rotation, mass loss) is excluded, so the central conclusion outruns the model grid.","rationale":"The reader's CONDITIONAL verdict is well founded. The strongest claim is interesting and partly supported by earlier work (Temaj et al. 2024; Burrows et al. 2024), and the paper is transparent about its limitations. My stress-test does not find an internal inconsistency; rather, it finds that the breadth of the central claim exceeds what the model grid can establish. The grid varies mass-accretion amount and phase but holds the stellar physics fixed: no rotation, no magnetic fields, no chemical mixing during merger, always net mass gain. Those are the very processes that distinguish real binary products. The paper's statement that these omissions do not affect the results is an assertion, not a demonstration, because the SN engine uses the entire pre-SN structure and the omitted processes can alter that structure at fixed sc. A targeted test with merger-realistic structures is feasible and would settle the question. Since the concern is exactly the kind of limitation that motivates a conditional acceptance, the reader's verdict should remain CONDITIONAL; I therefore recommend UNCHANGED. I partially agree with the reader's weakest_assumption: we both flag the merger approximation, but the reader also foregrounds the engine calibration, which I consider secondary because the paper explicitly discloses the structural MNi-Eexpl coupling and 3D simulations support the qualitative correlations.","tokens_in":66170,"tokens_out":7195,"duration_ms":83382,"concrete_test":"Take representative merger remnants from 3D hydrodynamic simulations or from 1D models with helium mixing and rotation at the same metallicity, relax them to iron core collapse with the same MESA configuration, and apply the same Müller et al. (2016) SN engine. Then compare (Eexpl, MNi, MNS) against the fiducial tracks in Fig. 1 at matched central entropy: if the remnants lie within the quoted scatter (≈0.4×10^51 erg, ≈0.02 M_sun, ≈0.05 M_sun), the history-independence claim survives; if they deviate systematically, the claim must be restricted to thermal-timescale accretors.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Sect. 3.1 the paper concludes that 'the past evolutionary histories of pre-SN stars do not matter much for the exact SN explosion outcome but rather only the pre-SN core structure as summarised here by the central specific entropy.' The support for this is a grid in which every accretor and merger is 'approximated by accretion onto single-star models with the momentary thermal-timescale mass accretion rate.' As Sect. 2 acknowledges, accretion on a thermal timescale is not adequate for Case-A mass transfer or for mergers, merger mixing is not captured, rotation is neglected, and late Case-B/C mergers can lose net mass and produce progenitors outside the grid. The paper asserts that these uncertainties 'do not affect our results, because we do not model individual binary systems but only effective mass accretion events of certain masses,' but that response does not test whether a genuine merger remnant with a mixed, spinning, magnetized core at the same central entropy would yield the same Eexpl, MNi, and MNS. Since the applied Müller et al. (2016) engine maps the full pre-SN interior structure into explosion outcomes, unmodelled differences in core composition, angular momentum, or magnetic fields can change the outcome at fixed sc. The central claim is therefore a statement about thermal-timescale accretors, not about stellar mergers.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper uses 419 MESA stellar models of single stars and binary mass accretors/mergers approximated by thermal-timescale accretion onto single-star models, passes their pre-SN structures through the parametric Müller et al. (2016) explosion engine, and reports correlations of explosion energy, nickel mass, NS kick velocity, and NS gravitational mass with central specific entropy and with each other. It assigns SN types (IIP, 1987A-like, IIn) by HR-diagram position, derives IIP plateau light-curve properties via Goldberg et al. (2019) scalings, and compares the resulting properties and rates with observations, including long-plateau IIPs, 87A-like SNe, and luminous interacting SNe. The central claim is that explosion outcomes depend on the pre-SN core structure summarized by central entropy, not on whether the star evolved as a single star, an accretor, or a merger product.","tokens_in":66565,"tokens_out":5478,"duration_ms":64319,"significance":"If the correlations hold, the paper offers a compact predictive framework for SN outcomes and a physical explanation for the diversity of hydrogen-rich SNe from binary products. The strength of the paper is its large, systematic grid, the explicit treatment of many caveats, and the public availability of model data. The correlations with central entropy and the MNi–Eexpl and MNi–MNS relations are useful and will likely be widely cited. However, the manuscript's headline history-independence claim is tested only for thermal-timescale accretors, and the MNi–Eexpl relation is partly inherited from the assumed explosion engine; these caveats limit the strength of the conclusions as currently stated. I regard the central physics as defensible but in need of reframing and additional quantitative support.","major_comments":[{"comment":"The history-independence claim is not supported for actual stellar mergers. Every 'merger' in the grid is approximated by thermal-timescale accretion onto a non-rotating, unmixed single-star model, as stated in Sect. 2, where the paper acknowledges that Case-A accretion, merger mixing, rotation, magnetic fields, and net mass loss are not captured. Because the Müller et al. (2016) engine maps the full pre-SN interior structure into Eexpl, MNi, and MNS, a genuine merger remnant with a mixed, rotating, magnetized core could plausibly give different outcomes at the same central specific entropy. The Sect. 3.1 statement that 'the past evolutionary histories of pre-SN stars do not matter much for the exact SN explosion outcome but rather only the pre-SN core structure as summarised here by the central specific entropy' therefore overstates the scope of the test; it should be phrased as a statement about thermal-timescale accretors, or supported by additional models that include merger-specific physics or by a quantitative argument that the missing physics cannot change the correlations.","section":"Sect. 2 and Sect. 3.1"},{"comment":"The MNi–Eexpl correlation is largely built into the applied SN model rather than being an independent prediction. The paper states in Sect. 3.1 that 'this very connection of explosion energy and nickel yield via the post-shock temperature is implemented in the Müller et al. (2016) SN code applied here and thus explains the found correlation.' Consequently, Eq. (1) reflects the assumed engine calibration, and the abstract's phrase 'We find linear relations between the nickel mass and the SN explosion energy' should be accompanied by this caveat. Sect. 3.2 already notes the quantitative dependence on calibrations, but the framing in the abstract and conclusions should be similarly explicit, since the relation's existence is inherited rather than newly established by this work.","section":"Sect. 3.1 and Sect. 3.2, Eq. (1)"},{"comment":"The claimed rough compatibility of the model SN IIn rate with observations is not robust as presented. Equation (7) depends on the uncalibrated choices Mξ−peak ≈ 22 M⊙, ΔMξ−peak = 2 M⊙, MIbc = 30 M⊙, and MSN = 8 M⊙, and the paper gives 7% without exploring the sensitivity to these thresholds. Since this rate comparison is one of the paper's main observational tests, the estimate should be presented as an illustrative range with the adopted values varied, or with a transparent justification that the result is insensitive to them.","section":"Sect. 4.3, Eq. (7)"}],"minor_comments":[{"comment":"The caption states 'Ejected nickel mass MNi (a) and squared SN velocity (vFe,50)^2 (b)', but the text in Sect. 3.5 refers to Fig. 9a when discussing the velocity–luminosity relation and Fig. 9b when discussing nickel mass; the panel labels or the caption order should be corrected.","section":"Fig. 9 caption"},{"comment":"The claim of 'no obvious relation' between explosion properties and evolutionary history is based on Pearson correlation coefficients and visual comparison of quadratic fits; reporting the residual scatter separately for single stars and for each accretor case would make the history-independence claim more quantitative and easier to assess.","section":"Sect. 3.1"},{"comment":"The ad hoc 10^4 yr LBV-residence threshold is used to flag many models throughout the paper; a one-sentence sensitivity test or a justification in terms of the implied mass loss would help the reader judge how much weight to place on the flagged models.","section":"Sect. 3.3"},{"comment":"The sentence that the uncertainties in merger mass loss 'do not affect our results' is stronger than the surrounding discussion warrants: the same paragraph notes that late Case-B/C mergers can lose mass and produce progenitors (e.g., SN IIb) outside the grid, so the statement should be softened to clarify that it applies only to the effective mass-accretion events being modeled.","section":"Sect. 2"}],"recommendation":"major_revision","confidential_remarks":"The paper is well within the scope of A&A and the modeling effort is solid. The main issue is that the central history-independence conclusion is framed more broadly than the model grid can support, and the MNi–Eexpl relation is partly an artifact of the assumed explosion engine. Both issues can be fixed by reframing and by adding sensitivity estimates, so major revision rather than rejection seems appropriate. I would also ask the authors to make the SN IIn rate calculation in Eq. (7) more transparent regarding its dependence on the adopted mass cuts."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Fair take: solid and useful, with a real caveat on the headline claim. The paper applies the Müller+16 parametric engine to the 419-model grid from Paper I and maps out Eexpl, MNi, MNS, and kicks for single stars and accretors/mergers. The most valuable new pieces are the systematic demonstration that accretors/mergers produce long-plateau Type IIP SNe from low-CO-core, high-envelope-mass progenitors, and the quantitative MNi–MNS relation (Eq. 2) as a potential observational diagnostic. The model table and Zenodo data are a useful resource for the community.\n\nThe MNi–Eexpl correlation is less of a discovery: the paper itself notes that the connection is implemented in the Müller+16 engine, so the tight correlation is partly structural. That is handled honestly, but it should temper how the relations are quoted. Similarly, the history-independence claim in Sect. 3.1 is only tested for thermal-timescale accretion onto non-rotating, unmixed single-star models. True mergers involve mixing, rotation, magnetic fields, and possibly net mass loss, none of which are in the grid. The authors' response that they are modeling effective mass accretion events is fair for a first pass, but it means the central claim is a statement about a restricted class of models, not about stellar mergers in general. The paper would be stronger if that limitation were carried more explicitly into the conclusions.\n\nThe SN-type classification is admittedly ad hoc, the 10^4 yr LBV flag is arbitrary, and final masses are upper limits; all are acknowledged, so they are minor. The comparison to observations is reasonable and appropriately cautious about degeneracies.\n\nBottom line: this deserves a serious referee. I would ask for a clearer statement of the validity domain of the history-independence claim, a sensitivity test of the typing scheme, and an attempt to anchor the MNi–MNS relation with independent SN models or observations. With those revisions, it would be a solid reference for SN progenitor work. I would cite it.","headline":"Useful and honest extension of the Paper I grid, but the history-independence claim is only tested within the thermal-timescale accretion approximation and the MNi–Eexpl relation is partly built into the engine; still deserves referee time.","tokens_in":67030,"tokens_out":2493,"would_cite":true,"duration_ms":27854,"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":"For hydrogen-rich supernovae, the explosion energy, nickel yield, and neutron-star kick are set by the pre-collapse core's central specific entropy, not by the star's binary past.","keywords":["binary mass transfer","stellar mergers","Type II supernovae","core-collapse supernovae","central specific entropy","neutron star kicks","SN 1987A-like supernovae","interacting supernovae"],"falsifier":"Find a single Type II supernova whose progenitor is well characterized so its pre-collapse central entropy is pinned down by a stellar model, and whose nickel mass, explosion energy, and neutron-star mass are all measured, the last from a bound binary after the explosion: if it falls off the paper's $s_c$ relations or the $M_{\\rm Ni}$-$M_{\\rm NS,grav}$ line by much more than the quoted scatter, the claim that history does not matter fails. A more direct test is a genuine merger simulation followed to collapse, since a merged star with the same central entropy as a single star of identical core mass that explodes with a clearly different energy in a full neutrino-hydrodynamics run would break the core-structure-only picture.","tokens_in":65913,"feed_emoji":"💥","tokens_out":11784,"duration_ms":116123,"temperature":0.7,"pith_summary":"Most massive stars exchange mass with or merge into a companion, so most hydrogen-rich (Type II) supernovae probably come from binary products rather than genuine single stars. This paper asks whether those products explode differently, and its answer is largely no: once the pre-supernova core structure is fixed, the explosion energy, nickel yield, neutron-star kick, and remnant mass are the same regardless of whether the star evolved alone, accreted matter during Case A, B, or C mass transfer, or passed through a long-lived blue-supergiant phase. A single summary variable, the central specific entropy of the core at collapse, tracks the explosion outcomes, and the paper derives relations linking the ejected nickel mass to both the explosion energy and the neutron-star mass. These relations matter because nickel is observable in supernova light-curve tails, so they open a route from photometry to explosion energy and remnant mass. The same models also populate three observed supernova classes, reproducing long-plateau Type IIP explosions with large envelopes but small CO cores (e.g., SN 2015ba) and offering candidate progenitors for interacting SNe IIn.","feed_headline":"Blast energy obeys core entropy, not the star's life story","feed_subtitle":"Measured nickel yields could reveal neutron-star masses, and swallowed companions explain long-plateau supernovae.","key_machinery":"The load-bearing instrument is the parametric neutrino-driven explosion model that takes the entire interior structure of each star at iron-core collapse as input and returns the explosion energy, nickel yield, neutron-star kick, and remnant mass, calibrated to the stellar models as described in the methods. The organizing variable is the central specific entropy $s_c$, the entropy per nucleon at the star's center, which collapses the many ways a star can be assembled into one number that predicts the explosion; the iron-core mass and the compactness parameter $\\xi_{2.5}$ serve as interchangeable summary proxies. The second key mechanism is the physical chain linking nickel to explosion energy and remnant mass: the explosion energy sets the post-shock temperature, which decides how much ejecta is explosively burned to nickel, while the binding energy governing explodability also tracks the location of shock revival and hence the neutron-star mass. Finally, the SN classification is made by the pre-supernova position in the Hertzsprung-Russell diagram, with cool supergiants below $\\log L/L_\\odot = 5.5$ assigned to SNe IIP, hotter compact stars to SN 1987A-like events, and luminous or LBV-region stars to interacting SNe IIn.","core_discovery":"The paper's central claim is that for hydrogen-rich Type II supernovae from accretors and mergers, the explosion outcome, meaning the explosion energy $E_{\\rm expl}$, nickel mass $M_{\\rm Ni}$, neutron-star kick velocity, and gravitational mass of the neutron star, is determined by the pre-supernova core structure, summarized by the central specific entropy $s_c$, and shows no obvious dependence on the evolutionary history of the pre-supernova star. Single stars, Case A, B, and C accretors, and models that passed through a long-lived blue-supergiant phase all follow the same correlations with $s_c$; even the Case-A accretors with incomplete rejuvenation lie on the same trend. The paper further finds a tight linear relation between ejected nickel mass and neutron-star gravitational mass, $M_{\\rm NS,grav}/M_\\odot = (2.757 \\pm 0.045)\\, M_{\\rm Ni}/M_\\odot + (1.259 \\pm 0.005)$, and an exponential relation between nickel mass and explosion energy, both largely independent of evolutionary history. These relations are anchored in the physics of neutrino-driven explosions, where a harder-to-explode core requires more intense neutrino heating, producing a more energetic explosion that burns more material to nickel, and where the same binding-energy scale sets the revived-shock location and hence the remnant mass. The paper then groups its models by pre-supernova position in the Hertzsprung-Russell diagram into SNe IIP, SN 1987A-like, and interacting SNe IIn, finding that the first two classes share similar core structures and hence similar explosion properties but differ in envelope radius and mass, while the interacting class comes from more massive cores.","pith_inferences":["If the central-specific-entropy picture survives contact with more detailed explosion models, population synthesis of supernovae could be reduced to a mapping from one or two core summary variables to explosion outcomes, with all of Type II light-curve diversity residing in envelope properties rather than engine properties.","The same logic suggests a testable observational programme: for Type II SNe with well-measured nickel masses and independently determined neutron-star masses, such as neutron stars later found in binary systems, the linear $M_{\\rm Ni}$-$M_{\\rm NS,grav}$ relation predicts a tight trend, and a scatter well above the model's $0.05\\,M_\\odot$ would signal that rotation, magnetic fields, or merger mixin","Because the models treat mergers as pure mass accretion and omit helium mixing into envelopes, the fraction of post-main-sequence mergers that become long-lived blue supergiants, roughly 5-35% needed to match the observed 1987A-like rate, is a sharp test of how much mixing actually occurs in real stellar mergers."],"forward_implications":["Nickel masses measured from the tails of SN light curves give, through the derived relations, an estimate of the explosion energy to within about $0.3 \\times 10^{51}$ erg and the neutron-star gravitational mass to within about $0.05\\,M_\\odot$, potentially breaking long-standing degeneracies in SN IIP modelling.","Binary mass accretors and stellar mergers naturally produce SNe IIP with plateau durations up to roughly 250 d, large ejecta masses, and small CO cores, matching objects like SN 2015ba that single-star channels struggle to explain.","SNe IIP and SN 1987A-like events come from stars with similar cores and therefore similar explosion energy and nickel ranges; what distinguishes them is the envelope, extended convective red supergiants versus compact radiative blue supergiants.","The plateau luminosity-velocity relation that underpins the standardised candle method is essentially unchanged by binary history, so accretors and mergers should not introduce large systematics in cosmological distance determinations from SNe IIP.","If luminous cool supergiants at $\\log L/L_\\odot \\gtrsim 5.5$ shed mass through envelope instabilities before collapse, the predicted rate of interacting SNe IIn is compatible with the observed rate, and some $10^6\\,L_\\odot$ blue-supergiant merger products could be progenitors of SN 1961V-, SN 2005gl-, and SN 2010jl-like events."],"supporting_citations":[{"why":"Supplies the parametric neutrino-driven explosion engine that converts each pre-SN structure into explosion energy, nickel mass, kick, and remnant mass, the core instrument of the study.","marker":"Müller et al. (2016)"},{"why":"Provides the calibrations of the explosion engine, including the 2 $M_\\odot$ neutron-star/black-hole discriminator, and the single-star model grid on which the accretor models are built.","marker":"Schneider et al. (2021)"},{"why":"Contains the stellar models of single stars, accretors, and mergers, the definition of long-lived blue-supergiant phases, and the pre-SN core structures that this paper evolves to explosion.","marker":"Paper I"},{"why":"Establishes the central specific entropy as a summary proxy for pre-SN core structure and its correlation with neutron-star mass, the basis for the paper's organizing variable.","marker":"Temaj et al. (2024)"},{"why":"Quantifies the population rate of post-main-sequence plus main-sequence mergers among Type II SNe, grounding the claim that most SNe II are binary products.","marker":"Zapartas et al. (2019)"},{"why":"Foundational estimate that about half of all Type II SNe come from accretors and mergers, motivating the entire single-star versus binary-product comparison.","marker":"Podsiadlowski et al. (1992)"},{"why":"Gives the analytic scaling relations for plateau luminosity, plateau duration, and Fe II velocities used to predict SN IIP light-curve properties from the models.","marker":"Goldberg et al. (2019)"},{"why":"Provides the observations of SN 2015ba, a long-plateau event with high ejecta mass and weak oxygen lines, that the paper's accretor models naturally explain.","marker":"Dastidar et al. (2018)"},{"why":"Supplies the empirical luminosity limit of red supergiants used to define the enhanced-mass-loss regime that may produce SNe IIn.","marker":"Davies et al. (2018)"}],"fun_headline_variants":["Core entropy, not life story, sets supernova power","Explosion energy tied to core entropy, not stellar history","Nickel yield reveals neutron star mass in Type II SNe","Merged stars explode by core structure, not past lives","Supernova power set by core entropy, not binary past"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The results assume the parametric explosion engine correctly converts the pre-collapse core structure into explosion energy, nickel yield, neutron-star mass, and kick, and that modelling binary accretion and mergers as mass added on a thermal timescale to a single star, without merger mixing, captures the physics that matters.","fun_headline_variants_meta":{"raw":{"variants":["Core entropy, not life story, sets supernova power","Explosion energy tied to core entropy, not stellar history","Nickel yield reveals neutron star mass in Type II SNe","Merged stars explode by core structure, not past lives","Supernova power set by core entropy, not binary past"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000274,"raw_usage":{"total_tokens":1815,"prompt_tokens":1300,"completion_tokens":515,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":916,"completion_tokens_details":{"reasoning_tokens":432}},"tokens_in":916,"tokens_out":515,"duration_ms":5134,"temperature":1.0,"reasoning_tokens":432,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T19:05:06.936783+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Find a single Type II supernova whose progenitor is well characterized so its pre-collapse central entropy is pinned down by a stellar model, and whose nickel mass, explosion energy, and neutron-star mass are all measured, the last from a bound binary after the explosion: if it falls off the paper's $s_c$ relations or the $M_{\\rm Ni}$-$M_{\\rm NS,grav}$ line by much more than the quoted scatter, the claim that history does not matter fails. A more direct test is a genuine merger simulation followed to collapse, since a merged star with the same central entropy as a single star of identical core mass that explodes with a clearly different energy in a full neutrino-hydrodynamics run would break the core-structure-only picture.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the calibrations of the explosion engine, including the 2 $M_\\odot$ neutron-star/black-hole discriminator, and the single-star model grid on which the accretor models are built."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the central specific entropy as a summary proxy for pre-SN core structure and its correlation with neutron-star mass, the basis for the paper's organizing variable."},{"cited_title":"E., Justham, S., et al","cited_arxiv_id":null,"evidence_quote":"Quantifies the population rate of post-main-sequence plus main-sequence mergers among Type II SNe, grounding the claim that most SNe II are binary products."}],"review_version":1}