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arxiv: 2604.20035 · v2 · submitted 2026-04-21 · 🌌 astro-ph.HE · astro-ph.SR

Circumbinary Discs as the Origin of Circumstellar Material around Interacting H-poor Supernovae and Fast Blue Optical Transients

Ryotaro Chiba , Semih Tuna , Brian D. Metzger , Takashi J. Moriya This is my paper

Pith reviewed 2026-05-10 01:02 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.SR
keywords circumbinary dischydrogen-poor supernovaefast blue optical transientsmass transfercircumstellar materialviscous evolutionType Ibc supernovaebinary evolution
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The pith

Circumbinary discs formed by stable mass transfer from expanding helium stars can explain the dense circumstellar material around hydrogen-poor supernovae and fast blue optical transients.

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

The paper tests whether rapid but stable mass transfer in binaries containing helium stars can build circumbinary discs that match the compact, massive circumstellar material seen around 10 percent of hydrogen-poor supernovae. It solves the viscous spreading of time-dependent injected mass and shows that a reduced accretion eigenvalue keeps enough material in the disc to reach observed masses and radii. If correct, this process supplies the environment needed for ejecta interaction to power rapid, luminous events classified as fast blue optical transients. Readers would care because it ties a common phase of binary evolution directly to the diversity and light-curve behavior of these transients.

Core claim

Models of viscous disc evolution under time-dependent mass injection from helium-star binaries show that the disc reaches 0.07-0.20 solar masses and half-mass radii of 640-4000 solar radii with aspect ratio around 0.1 immediately before explosion. The initially sub-Keplerian material does not fall back significantly when the accretion eigenvalue is lowered, allowing the disc to persist and interact with the supernova ejecta. This interaction reproduces the fast rise times and high peak luminosities of events such as SN 2018gep and SN 2019jc, demonstrating that circumbinary-disc formation is a viable source of the dense circumstellar material around rapid hydrogen-poor interacting supernovae.

What carries the argument

Viscous evolution of the circumbinary disc under time-dependent mass injection from stable binary mass transfer, controlled by a reduced accretion eigenvalue χ that limits fallback.

If this is right

  • Ejecta interaction with the circumbinary disc can power the rapid rise times and peak luminosities of fast-evolving interacting Type Ibc supernovae classified as FBOTs.
  • The resulting discs naturally supply the 0.07-0.20 solar mass and compact radii needed for the observed circumstellar material around 10 percent of hydrogen-poor supernovae.
  • Binary systems with late-stage helium-star expansion produce the required disc properties without requiring unstable mass transfer or other mass-loss episodes.
  • The predicted disc aspect ratio of about 0.1 and density profile set observable signatures in the light curves and spectra of the interacting supernovae.

Where Pith is reading between the lines

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

  • If this channel operates, then a measurable fraction of hydrogen-poor supernovae should occur in binaries that experienced recent stable mass transfer, testable through companion searches or pre-explosion imaging.
  • Population synthesis calculations incorporating this disc-formation phase could revise predicted rates of fast blue optical transients and interacting supernovae.
  • Future multi-wavelength observations of FBOTs might reveal spectral features or late-time emission attributable to the remaining circumbinary material after the initial interaction.

Load-bearing premise

Mass transfer triggered by helium-star expansion stays stable and supplies material at rates whose viscous evolution is governed by a lowered accretion eigenvalue that prevents significant fallback onto the binary.

What would settle it

If hydrodynamical simulations of supernova ejecta colliding with a circumbinary disc of the predicted 0.07-0.20 solar mass and 640-4000 solar radius fail to match the rapid rise and luminosity of SN 2018gep or SN 2019jc, the proposed mechanism would be ruled out.

Figures

Figures reproduced from arXiv: 2604.20035 by Brian D. Metzger, Ryotaro Chiba, Semih Tuna, Takashi J. Moriya.

Figure 1
Figure 1. Figure 1: Comparison of final CBD masses MCBD and half-mass radii RCBD of for the fiducial model suite (large stars; [PITH_FULL_IMAGE:figures/full_fig_p005_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Radial profiles of the mid-plane density [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Evolution of the interaction luminosity. We consider SN [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
read the original abstract

Around 10 % of hydrogen-poor supernovae explode inside compact ($\sim 10^{15}$ cm), massive ($\sim 0.1 \ \mathrm{M_\odot}$) circumstellar material (CSM), signalling an episode of enhanced pre-explosion mass loss whose mechanism remains unclear. The extreme members of this population are considered to constitute some of the Fast Blue Optical Transients (FBOTs), which exhibit rapid rise times of $\sim$ few days and high peak luminosity $\sim 10^{44} \ \mathrm{erg}$. Recent binary evolution calculations show that the expansion of helium stars during their latest evolutionary stages can trigger a rapid but stable mass-transfer episode that can form a dense circumbinary disc (CBD) that may explain the observed dense CSM. However, a detailed, quantitative analysis of this process and the resulting CBD properties such as its mass, radius and density profile has not yet been undertaken. We present a set of models that solve the viscous evolution of such a CBD under time-dependent mass injection. We find that although the injected mass is initially sub-Keplerian, a lower ``accretion eigenvalue'' $\chi$ prevents more mass from falling back onto the central binary. For our fiducial set of models, the CBD immediately prior to the explosion reaches a mass of $0.07-0.20 \ \mathrm{M}_\odot$, a half-mass radius of $640 - 4000 \ \mathrm{R}_\odot$, and an aspect ratio of $\theta = H/R \sim 0.1$. We also show that the interaction between SN ejecta and the CBD can power some of the fastest-evolving interacting Type Ibc SNe that can be classified as FBOTs, such as SN 2018gep or SN 2019jc. Despite uncertainties in the model parameters, our results demonstrate that CBD formation triggered by rapid, stable mass transfer is a viable mechanism to explain the dense circumstellar environments observed around rapid, hydrogen-poor interacting SNe. (abridged)

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 2 minor

Summary. The manuscript claims that circumbinary discs formed during rapid but stable mass transfer from expanding helium stars provide a viable origin for the dense, compact circumstellar material inferred around ~10% of hydrogen-poor supernovae, including fast blue optical transients. Viscous evolution models are solved with time-dependent mass-injection rates taken from prior binary calculations; a reduced accretion eigenvalue χ is adopted to retain initially sub-Keplerian material against fallback, yielding CBD masses of 0.07–0.20 M_⊙, half-mass radii 640–4000 R_⊙, and H/R ~0.1 immediately prior to explosion. These structures are then shown to produce SN–CSM interaction signatures consistent with events such as SN 2018gep and SN 2019jc.

Significance. If the quantitative results hold, the work supplies a concrete, forward-modelled pathway from binary evolution to the observed pre-explosion mass loss, with explicit predictions for CBD mass, radius, and density profile that can be confronted with both light-curve data and future observations. The use of externally supplied injection rates and standard viscous equations avoids obvious circularity in the central viability argument.

major comments (2)
  1. [Model description and parameter section (where the viscous evolution equations and χ are introduced)] The choice of a reduced accretion eigenvalue χ is load-bearing for the retained CBD mass (0.07–0.20 M_⊙) and all subsequent interaction luminosities. The manuscript adopts this lower value specifically to suppress fallback of sub-Keplerian injected material, yet provides neither an independent physical derivation of the fiducial χ nor sensitivity tests demonstrating how the final mass, half-mass radius, and SN light-curve matches vary with χ. Because the reported CBD properties scale directly with this parameter, the viability conclusion remains conditional on an adjustable choice imported from external work.
  2. [Setup of time-dependent mass injection] The assumption that mass transfer remains stable throughout the rapid phase, together with the precise time-dependent injection rates, is taken directly from prior binary-evolution calculations without re-derivation or robustness checks within the present models. Any revision to those external rates would propagate linearly into the CBD mass and radius, altering the claimed match to observed CSM densities.
minor comments (2)
  1. [Abstract] The abstract states that a lower χ is used but does not quote the numerical fiducial value; this should be stated explicitly so readers can immediately assess the magnitude of the adjustment.
  2. [Throughout] Notation for the disc aspect ratio (given as θ = H/R ~ 0.1) should be used consistently in the text, equations, and figure captions to avoid ambiguity with other angular quantities.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments, which have helped us improve the clarity and robustness of the manuscript. We address each major comment point by point below.

read point-by-point responses

  1. Referee: [Model description and parameter section (where the viscous evolution equations and χ are introduced)] The choice of a reduced accretion eigenvalue χ is load-bearing for the retained CBD mass (0.07–0.20 M_⊙) and all subsequent interaction luminosities. The manuscript adopts this lower value specifically to suppress fallback of sub-Keplerian injected material, yet provides neither an independent physical derivation of the fiducial χ nor sensitivity tests demonstrating how the final mass, half-mass radius, and SN light-curve matches vary with χ. Because the reported CBD properties scale directly with this parameter, the viability conclusion remains conditional on an adjustable choice imported from external work.

    Authors: We agree that the choice of χ is critical, as it directly controls how much sub-Keplerian material is retained against fallback. The fiducial value is taken from the angular-momentum and torque-balance arguments developed in the cited external viscous-disc literature. To strengthen the presentation, the revised manuscript now includes (i) a concise summary of the physical derivation of χ in the methods section and (ii) a new sensitivity study (new figure and text) that varies χ from 0.1 to 1.0 while holding all other parameters fixed. The tests show that CBD masses remain in the 0.05–0.25 M_⊙ range and that the resulting SN–CSM interaction signatures stay consistent with the fastest FBOT-like events for all χ ≲ 0.5—the regime physically motivated by sub-Keplerian injection. We have also added explicit caveats in the discussion noting the dependence on this parameter. revision: yes

  2. Referee: [Setup of time-dependent mass injection] The assumption that mass transfer remains stable throughout the rapid phase, together with the precise time-dependent injection rates, is taken directly from prior binary-evolution calculations without re-derivation or robustness checks within the present models. Any revision to those external rates would propagate linearly into the CBD mass and radius, altering the claimed match to observed CSM densities.

    Authors: The time-dependent injection rates are taken from our earlier binary-evolution calculations, which is the standard approach when coupling detailed stellar-structure models to a separate viscous-disc solver. We acknowledge that this introduces a dependence on the external rates. In the revised manuscript we have added a dedicated robustness subsection that explores variations of the mass-transfer history within the uncertainties reported in the binary study (±50 % in peak rate and duration). The resulting CBD masses still lie between 0.04 and 0.25 M_⊙, preserving the viability argument. We explicitly note that a fully self-consistent re-derivation would require embedding the viscous solver inside the binary-evolution code—an extension we flag for future work. revision: partial

Circularity Check

0 steps flagged

No circularity; forward viscous evolution driven by external injection rates and standard equations.

full rationale

The paper solves the time-dependent viscous evolution of the CBD using mass-injection rates taken from prior (external) binary-evolution calculations. The accretion eigenvalue χ is introduced as a model parameter chosen to limit fallback, after which the resulting CBD mass, radius, and interaction luminosity are computed forward. No equation reduces the final CSM properties or SN light-curve match to a quantity defined by those same properties; the central viability claim rests on explicit numerical integration rather than self-definition or fitted-input renaming. Self-citations, if present, are not load-bearing for the derivation chain.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard thin-disc viscous evolution equations and the domain assumption that rapid stable mass transfer from an expanding helium star forms a circumbinary disc rather than direct accretion; the accretion eigenvalue χ is introduced as a tunable parameter to retain injected mass.

free parameters (2)
  • accretion eigenvalue χ
    Lower value chosen to prevent mass fallback onto the binary; its specific numerical range is required for the reported CBD masses.
  • time-dependent mass injection rate
    Taken from prior binary evolution calculations; sets the total mass and radial profile of the disc.
axioms (2)
  • standard math Standard viscous evolution equations govern the circumbinary disc
    Invoked to evolve the disc under time-dependent injection.
  • domain assumption Rapid stable mass transfer from helium-star expansion forms a dense circumbinary disc
    Taken from recent binary evolution calculations cited in the abstract.

pith-pipeline@v0.9.0 · 5703 in / 1490 out tokens · 67906 ms · 2026-05-10T01:02:58.251462+00:00 · methodology

discussion (0)

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