Same explosion, many faces: numerical modeling reveals viewing angle as a driver of diversity for core-collapse SNe in binary systems

Irene Salmaso; Maryam Modjaz; Poonam Chandra; Raphael Baer-Way; Shazrene Mohamed; Soham Mandal

The same core-collapse supernova in a binary can look like very different events depending on viewing angle, because binary mass loss builds highly aspherical circumstellar material.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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Stable Roche-lobe overflow builds equatorially enhanced CSM so that one CCSN explosion yields light curves differing by factors of ~5 in peak luminosity and ~1.5 mag in late B−V by viewing angle, biasing 1D spherical fits by tens to hundreds of percent.

T0 review reviewed 2026-07-31 challenge →

load-bearing objection End-to-end MESA→3D L2 CSM→angle-dependent Stella pipeline shows real orientation-driven diversity and 1D-fit bias; the factor-of-5 / 50% / >200% numbers rest on 1D rays and a tiny grid. the 2 major comments →

arxiv 2607.28519 v2 pith:M6L5BYCD submitted 2026-07-30 astro-ph.HE

Same explosion, many faces: numerical modeling reveals viewing angle as a driver of diversity for core-collapse SNe in binary systems

Soham Mandal , Raphael Baer-way , Shazrene Mohamed , Irene Salmaso , Poonam Chandra , Maryam Modjaz This is my paper

classification astro-ph.HE

keywords stellar evolutionmassive starssupernovaecircumstellar mediumradiation hydrodynamicsbinary interactionType II supernovaeviewing-angle effects

verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The reading

Many core-collapse supernova progenitors live in binaries, so pre-explosion mass transfer can reshape both the star and the gas around it. This paper follows wide binaries through stable Roche-lobe overflow, builds three-dimensional maps of the lost gas, and then computes light curves along polar, oblique, and equatorial sightlines. It finds that the circumstellar material is strongly equatorially concentrated, so the same explosion can differ by factors of several in peak luminosity and by about 1.5 magnitudes in late-time color purely with observer orientation. Fitting those light curves with standard one-dimensional models that assume isolated stars and spherical winds can misestimate explosion properties by up to about 50 percent and mass-loss rates by more than a factor of two. The claim is that a large share of interacting Type II diversity may be geometry and viewing angle, not a zoo of unrelated explosions, which is why multi-dimensional interpretation matters.

Core claim

Stable late-stage Roche-lobe overflow in massive binaries builds dense, equatorially enhanced circumstellar material through non-conservative L2 outflow. When the donor explodes into that medium, ejecta–CSM interaction produces strong viewing-angle dependence: peak luminosities can differ by factors of about five and late-time B−V by about 1.5 mag between polar and equatorial sightlines. The same event can therefore occupy different observed subclasses of interacting Type II supernovae, and spherical one-dimensional inference frameworks can bias explosion parameters by up to ~50% and mass-loss rates by >200%.

What carries the argument

The end-to-end pipeline that turns binary evolution into angle-dependent light curves: MESA binary tracks supply mass-loss history and orbit; Sprout builds the 3D L2-driven CSM; density columns at 0°, 45°, and 90° are appended to the ejecta and exploded in Stella. That chain is what converts binary parameters into quantitative viewing-angle diversity and into the bias estimates against spherical-wind grids.

Load-bearing premise

The central numbers rest on treating multi-dimensional ejecta–CSM interaction as independent one-dimensional radiation-hydro runs along extracted radial sightlines, which the paper itself flags as least reliable in the first ~10 days.

What would settle it

Late-time multi-band (especially blue/UV) light curves and colors for a well-observed interacting Type II, combined with independent geometry constraints (spectropolarimetry or resolved CSM structure), that fail to show the predicted polar-versus-equatorial contrast—brighter, bluer, longer-lived interaction and spiral-driven undulations only for dense equatorial sightlines—while explosion energy and nickel mass are held fixed.

Watch this falsifier. Get emailed when new claim-graph text bears on it.

If this is right

A single binary explosion can be classified as different interacting Type II subtypes solely by orientation.
Inferred ZAMS mass, explosion energy, nickel mass, and especially mass-loss rate from spherical wind grids can be systematically wrong for binary-shaped CSM.
Late-time blue/UV monitoring is the most sensitive probe of asymmetric binary-driven CSM.
Population rates of late Case C mass transfer (~few percent of CCSNe) are large enough that binary geometry can supply a substantial share of the interacting CCSN sample.
Inference frameworks need multi-dimensional or at least angle-aware CSM models rather than isolated spherical winds.

Where Pith is reading between the lines

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

If orientation dominates, surveys that lack late-time UV coverage will systematically undercount equatorial interaction and mis-map the true mass-loss distribution.
Spectropolarimetric time series that track the transition from early multi-D shock geometry to homologous ejecta would be a direct test of when the 1D-column approximation becomes safe.
Extending the same pipeline to common-envelope and merger channels would show whether the viewing-angle lever arm is even larger for dynamically ejected CSM.
Host-metallicity trends in interacting SN rates may partly reflect binary mass-transfer efficiency, not only single-star wind strength.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Desk Editor's Note

End-to-end MESA→3D L2 CSM→angle-dependent Stella pipeline shows real orientation-driven diversity and 1D-fit bias; the factor-of-5 / 50% / >200% numbers rest on 1D rays and a tiny grid.

read the letter

The new piece is the coupled product: stable Case B/C RLOF mass-loss histories from MESA, mapped through 3D L2/spiral CSM in Sprout, then Stella light curves on three extracted rays, plus a concrete Moriya-grid bias table. Pieces exist separately (Pejcha/Scherbak hydro, Vlasis/Suzuki multi-D SN–CSM, Moriya 1D grids); the end-to-end quantitative demonstration does not.

What they do well is clear. The binary evolution is standard and careful (non-conservative β_eff, L2 angular momentum from Scherbak). The CSM morphology is solid—equatorially enhanced spirals, polar density steepening to ~r^{-4}, velocity contrasts of tens of km/s (Figs. 5–6). Photosphere diagnostics (§3.4) show early angular differences and later convergence near recombination, which is honest. Late blue excess, equatorial undulations from the spiral, and the shape-only matches to 2023ixf / 2019zrk / 2024hpj are useful. Table 2 is the practical payoff: same explosion, different θ, ZAMS/E_exp/Ṁ inferences swing hard under spherical-wind assumptions. Circularity is low; E and Ni are fixed a priori.

Soft spots are real but proportionate. The grid is tiny (fixed 16 M⊙ primary, handful of qi–Pi). The load-bearing step is independent 1D Stella columns for a 3D interaction. The paper itself flags multi-D transport and non-radial shocks at t≲10 d and notes photospheric quantities only converge ~30 d; the late-time L contrast, B−V swing, and bias percentages still assume the rays stay energetically decoupled. If lateral transport reduces contrast, the abstract’s ~5 / 1.5 mag / 50% / >200% and “substantial fraction” language over-reach. Observational comparisons are shape-only; absolute L and decline times do not match. No public inlists.

This is for people who model interacting SNe or recover mass-loss rates from light curves. It deserves a serious referee. I would engage, cite the morphology and the bias warning, and treat the exact percentages as upper bounds until a multi-D RT check or wider grid appears. Send it out.

Referee Report

2 major / 5 minor

Summary. The paper models core-collapse SNe from massive binaries undergoing stable Roche-lobe overflow. A small MESA grid with fixed 16 M⊙ primary and selected qi–Pi combinations produces non-conservative L2 mass loss; Sprout then builds 3D aspherical CSM; angle-dependent density columns (θ = 0°, 45°, 90°) are appended to MESA ejecta and exploded with Stella. The resulting light curves show strong viewing-angle dependence (peak luminosities differing by factors of ~5, late-time B−V by ~1.5 mag). Fitting the same light curves with a spherical Type II grid (Moriya et al. 2023) yields biases up to ~50% in explosion parameters and >200% in mass-loss rates. The authors argue that binary-shaped CSM plus orientation can account for a substantial fraction of interacting Type II diversity.

Significance. If the quantitative claims hold, the work supplies a concrete, physically motivated channel linking binary evolution to the observed continuum of interacting Type II light curves and demonstrates that standard 1D spherical-wind inference can be systematically biased. The pipeline (MESA → Sprout → multi-angle Stella) is a useful step toward connecting binary population synthesis to multi-D observables, and the explicit comparison to Moriya-grid fits (Table 2) makes the bias claim falsifiable. The qualitative demonstration of equatorially enhanced L2 CSM and spiral density undulations is on firm ground and will be of interest even if the precise numerical factors are later revised by full multi-D radiation hydrodynamics.

major comments (2)

[§3.4, §3.5, §4.2, Table 2, abstract] The central quantitative claims (peak L differing by ~5, late B−V by ~1.5 mag, explosion-property biases ~50%, Ṁ biases >200%; abstract, §3.5, §4.2, Table 2) rest on independent 1D Stella runs along density columns extracted from 3D Sprout CSM (pipeline Fig. 2; §2.3). Section 3.4 itself states that multi-D radiation transport and non-radial shocks can redistribute energy in ways absent from radial-column treatments, that this is most severe at t ≲ 10 d, and that photospheric R/v/T only converge near recombination (~30 d). Late-time equatorial undulations, blue excess (Fig. 9), and the Moriya-grid fits that supply the bias percentages (Fig. 12, Table 2) still assume those columns remain energetically decoupled. The manuscript needs a clearer quantification of residual lateral-transport uncertainty after ~10 d (or an explicit statement that the quoted factors are upper bounds under the 1D-
[Table 1, §2.1, abstract, §5] The model grid is extremely narrow: fixed primary mass 16 M⊙, solar metallicity, only a handful of (qi, Pi) points, and explosion energy and 56Ni fixed a priori (Table 1, §2.1.5). While the paper is framed as exploratory, the abstract and conclusion generalize to “a substantial fraction of interacting Type II SN diversity” and cite population-synthesis rates (~5%). The diversity and bias claims should be explicitly caveated as applying to the Case-C RLOF subset explored here; otherwise the leap from a few systems to the observed landscape is not supported by the calculations presented.

minor comments (5)

[abstract, §3.5, Fig. 9] Abstract and §3.5 quote peak-luminosity contrasts of ~5, yet the bolometric panel of Fig. 9 and the text of §3.5 describe more modest bolometric variation, with the largest contrast appearing in UV. Clarify which band/epoch supplies the factor-of-~5 number.
[Table 2] In Table 2 the true terminal mass-loss rates are given only in the table note; adding a column of “true” Ṁ (or M_CSM) next to the inferred values would make the >200% bias claim immediately verifiable.
[Fig. 11, §4.1] Figure 11 comparisons are qualitative and absolute luminosities/decline times are not reproduced; the caption or text should state more explicitly that only morphological similarity is claimed.
[title page, throughout] Typographical inconsistencies: “V A” vs “VA” in affiliations; occasional missing spaces before citations; “RSGS” vs “RSGs”.
[Table 1] The expected SN type column in Table 1 is based solely on envelope mass and explicitly excludes CSM interaction; a short clarifying sentence in the table note would prevent misreading.

Circularity Check

0 steps flagged

No significant circularity: forward binary–CSM–light-curve pipeline; diversity and fit biases are simulation outputs, not inputs.

full rationale

The paper’s chain is standard forward modeling: MESA binaries with fixed ZAMS primary, fixed E_exp = 10^51 erg and M_Ni = 0.04 M_⊙ from the literature (not tuned to the diversity claim), L2 mass-loss histories fed into Sprout 3D hydro, angle-extracted density columns exploded in Stella, then synthetic bolometric LCs fit post hoc with the external Moriya et al. (2023) Type II grid to quantify inference bias. Peak-luminosity contrast, B−V spread, and the Table 2 percentage biases are measured outputs of that pipeline, not quantities fitted in and re-exported as predictions. Domain prescriptions (β_eff step function; h_loss ≈ 0.8 h_L2 from Scherbak et al. 2025) are modeling assumptions, not self-definitional closures. Self-citations (Sprout code) are tool references, not load-bearing uniqueness theorems. Qualitative SN comparisons do not set model parameters. No step reduces a claimed prediction to its own input by construction.

Axiom & Free-Parameter Ledger

6 free parameters · 6 axioms · 0 invented entities

The claim rests on standard stellar/binary physics plus several modeling closures that are not derived here: a step-function mass-transfer efficiency at critical rotation, L2 specific angular momentum and launch speed taken from external hydro, fixed explosion energy and nickel mass, polytropic 3D hydro without cooling/B-fields, and the substitution of independent 1D RT columns for multi-D transport. Free parameters are few and mostly discrete grid choices rather than continuous fits to the diversity signal.

free parameters (6)

Initial primary mass Md,i = 16 M⊙
Fixed by hand at 16 M⊙ for the entire suite; all diversity is explored only around this single ZAMS mass.
Explosion energy E_exp = 10^51 erg
Set to 10^51 erg for all models from literature distributions, not computed from the progenitor core.
56Ni mass M_Ni = 0.04 M⊙
Fixed at 0.04 M⊙ for all explosions; directly affects late light curves used in bias fits.
L2 outflow launch speed fraction = 0.01 r_L2 Ω
Radial velocity injected at L2 set to 0.01 of orbital speed at L2—an order-unity modeling choice.
L2 specific angular momentum factor = 0.8 h_L2
hloss = 0.8 h_L2 adopted from Scherbak et al. (2025) for near-unity q; controls equatorial collimation.
Mixing-length and overshoot parameters = α_MLT=1.5; ov=0.035/0.01 Hp
α_MLT=1.5, core overshoot 0.035/0.01 Hp, α_sc=1.0, α_th=2.0, rotational mixing multiplier 0.033—standard but chosen values that affect envelope structure and RLOF timing.

axioms (6)

domain assumption Mass-transfer efficiency β_eff equals 1 below critical accretor rotation and 0 at/above critical rotation (disk-mediated, non-conservative thereafter).
Eq. (1) and §2.1.4; closes 1D binary evolution and sets almost all CSM mass via L2.
domain assumption Stable RLOF (no common-envelope) for the chosen wide Pi and qi range; CEE channels omitted.
Stated in §2.1; selects only the stable Case B/C subset of binary outcomes.
ad hoc to paper Angle-dependent 1D radiation-hydro on extracted CSM columns is sufficient to predict multi-band light-curve diversity after ~10 days.
Core of the method (Fig. 2, §2.3, defended in §3.4); multi-D RT and non-radial shocks are acknowledged but not modeled.
domain assumption 3D CSM hydro with γ=5/3 ideal gas, no radiative cooling, no magnetic fields, quasi-steady after ~10 orbits.
§2.2; morphology and density contrast of the spiral CSM depend on these closures.
domain assumption Dutch wind prescription and solar metallicity Z=0.0154 adequately describe winds that remain subdominant to L2 loss.
§2.1.1–2.1.3; authors argue L2 rates exceed winds by orders of magnitude.
domain assumption Moriya et al. (2023) spherical Type II grid is a fair proxy for how observers infer explosion and CSM parameters.
§4.2 fitting procedure that produces the 50% / >200% bias numbers.

reviewed 2026-07-31 · how reviews work

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Cite this review

Pith. "Pith review of Same explosion, many faces: numerical modeling reveals viewing angle as a driver of diversity for core-collapse SNe in binary systems." pith.science (2026). https://pith.science/paper/M6L5BYCD

@misc{pith2026260728519,
  author       = {Pith},
  title        = {Pith review of: Same explosion, many faces: numerical modeling reveals viewing angle as a driver of diversity for core-collapse SNe in binary systems},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/M6L5BYCD}},
  note         = {Machine review of arXiv:2607.28519}
}

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read the original abstract

Observable properties of core-collapse supernovae (CCSNe) depend sensitively on the circumstellar material (CSM) formed by pre-explosion mass loss from the progenitor star. Since a large fraction of CCSN progenitors reside in binaries, both the progenitor structure and surrounding CSM can be significantly impacted by binary interaction. Yet, its impact on the observed CCSN landscape remains poorly constrained. In this work, we investigate CCSNe from binary systems undergoing stable Roche lobe overflow. We construct a suite of binary evolution models in \texttt{MESA} with a fixed initial primary mass ($16M_{\odot}$), exploring secondary masses in the range $12-15M_{\odot}$ and initial orbital periods $>500$ days. We generate three-dimensional (3D) CSM structures from the resulting mass-loss histories and orbital dynamics, extract angle-dependent density profiles along three lines of sight, and compute multi-band light curves with the radiation-hydrodynamics code \texttt{Stella}. We find that binary-driven CSM develops highly aspherical morphologies, governed by the orbital period and the mass ratio. Interaction between SN ejecta and this structured medium produces pronounced viewing-angle dependence in the light curves, with peak luminosities differing by factors of $\sim5$ and late-time $B-V$ colors varying by $\sim1.5$ mag depending on observer orientation. We further show that interpreting such events with one-dimensional frameworks assuming isolated progenitors and spherical winds can introduce biases up to $50\%$ for inferred explosion properties and $>200\%$ for inferred mass-loss rates. Our results are consistent with a substantial fraction of interacting Type II SN diversity arising from binary-shaped asymmetric CSM and viewing-angle effects, motivating multidimensional approaches to interpreting these transients.