Dynamics and observational signatures of core-collapse supernovae with central engines: hydrodynamics simulations with Monte Carlo post-processing

Daniel Kasen; Kiran Eiden

arxiv: 2510.13741 · v4 · submitted 2025-10-15 · 🌌 astro-ph.HE

Dynamics and observational signatures of core-collapse supernovae with central engines: hydrodynamics simulations with Monte Carlo post-processing

Kiran Eiden , Daniel Kasen This is my paper

Pith reviewed 2026-05-18 07:06 UTC · model grok-4.3

classification 🌌 astro-ph.HE

keywords core-collapse supernovaecentral engineshydrodynamics simulationsradiation transportsupernova light curvesbroad-line Ic supernovaesupernova transientsRayleigh-Taylor instability

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The pith

Sufficiently powerful central engines break through supernova ejecta, mixing material and producing faster-rising light curves that resemble broad-line Ic supernovae.

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

This paper uses two-dimensional hydrodynamics simulations with Monte Carlo radiation transport post-processing to examine how a long-lived central energy source alters core-collapse supernova evolution. The engine excavates a central bubble that becomes Rayleigh-Taylor unstable and, when powerful enough, breaks out through rupture points to accelerate and compositionally mix the entire ejecta. This dynamical change opens low-density channels, allowing faster photon escape and quicker-rising optical light curves. Spectra begin hot and featureless but later match broad-line Ic supernovae, while variability in engine energy and injection rate may connect events across classes including fast blue optical transients and superluminous supernovae.

Core claim

A long-lived central engine embedded in expanding supernova ejecta excavates a bubble that becomes Rayleigh-Taylor unstable. Sufficiently powerful engines break through the bubble edge at distinct rupture points, accelerating, shredding, and compositionally mixing the ejecta. The resulting dynamical impact produces faster-rising optical light curves because photon escape is facilitated by faster expansion and low-density channels. For strong engines the spectra evolve from initially hot and featureless to resemble those of broad-line Ic supernovae, while high-velocity gas may produce radio emission and low-velocity central material may yield narrow emission lines resembling interacting-supem

What carries the argument

Two-dimensional hydrodynamics simulations of a prescribed central energy source with variable total energy, injection rate, and isotropy, followed by time-dependent Monte Carlo radiation transport, in which the engine-driven bubble undergoes Rayleigh-Taylor instability and breakout.

If this is right

Faster-rising optical light curves result from faster ejecta expansion and low-density channels opened by engine breakout.
Spectra start hot and featureless but later evolve to match broad-line Ic supernovae.
High-velocity gas outflowing from rupture points may produce observable radio emission.
Narrow emission lines from ionized low-velocity central material can escape under certain conditions and resemble features of interacting supernovae.
Variability in engine energy reservoir and injection rate produces heterogeneous events spanning fast blue optical transients, broad-line Ic supernovae, and superluminous supernovae.

Where Pith is reading between the lines

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

The compositional mixing could alter late-time spectroscopic signatures of heavy elements in the outer layers.
Rise-time measurements might be used to infer engine strength in observed events.
Three-dimensional extensions of the simulations could reveal additional instabilities that change the efficiency of ejecta shredding.

Load-bearing premise

The central engine is modeled as a prescribed, long-lived energy source whose total energy, injection rate, and degree of isotropy can be varied independently of the explosion itself.

What would settle it

Detection or non-detection of high-velocity radio-emitting outflows together with mixed ejecta compositions in supernovae that show unusually fast-rising light curves would confirm or refute the engine-breakout mixing scenario.

read the original abstract

A long-lived central engine embedded in expanding supernova ejecta can alter the dynamics and observational signatures of the event, producing an unusually luminous, energetic, and/or rapidly-evolving transient. We use two-dimensional hydrodynamics simulations to study the effect of a central energy source, varying the amount, rate, and isotropy of the energy deposition. We post-process the results with a time-dependent Monte Carlo radiation transport code to extract observational signatures. The engine excavates a bubble at the centre of the ejecta, which becomes Rayleigh-Taylor unstable. Sufficiently powerful engines are able to break through the edge of the bubble and accelerate, shred, and compositionally mix the entire ejecta. The breakout of the engine-driven wind occurs at distinct rupture points, and the outflowing high-velocity gas may eventually give rise to radio emission. The dynamical impact of the engine leads to faster rising optical light curves, with photon escape facilitated by the faster expansion of the ejecta and the opening of low-density channels. For models with strong engines, the spectra are initially hot and featureless, but later evolve to resemble those of broad-line Ic supernovae. Under certain conditions, line emission from ionized, low-velocity material near the centre of the ejecta may be able to escape and produce narrow emission similar to that seen in interacting supernovae. We discuss how variability in the engine energy reservoir and injection rate could give rise to a heterogeneous set of events spanning multiple observational classes, including the fast blue optical transients, broad-line Ic supernovae, and superluminous supernovae.

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.

Desk Editor's Note private letter to a colleague

This 2D hydro plus Monte Carlo paper shows that a strong central engine can rupture the ejecta bubble, mix material globally, and produce faster-rising light curves with later broad-line Ic spectra, but the engine is inserted as an independent tunable source.

read the letter

The main point is that sufficiently energetic engines in these runs break out of the central bubble, shred and mix the ejecta, and drive faster optical light curves while shifting the spectra toward broad-line Ic types at later times. The breakout also opens channels that help photons escape earlier. This comes from varying the engine energy, injection rate, and isotropy in 2D hydro, then feeding the results into time-dependent Monte Carlo transport for the observables. The combination of controlled parameter sweeps with radiation post-processing is the incremental step beyond prior 1D or analytic engine models. The qualitative outcomes line up with the setup: the bubble forms, Rayleigh-Taylor fingers grow, and strong cases rupture at points, accelerating outer material. Standard hydro and Monte Carlo methods are used, so the dynamical and radiative effects follow directly without hidden fitting. The discussion links the variations to a spread of transients including fast blue optical transients and superluminous events, which is a reasonable way to frame the results. The soft spot is the engine itself. It is prescribed as a long-lived source whose total energy and isotropy are set independently after the initial explosion, without deriving the injection history from collapse, accretion, or neutrino physics. That leaves open whether the strong-engine cases that produce full mixing actually occur in nature. The 2D geometry also limits how the instabilities and mixing develop, and the paper notes that 3D plus full transport would be needed for firmer numbers. This work is for supernova modelers who want to explore how engine parameters translate into observable changes in a controlled way. Readers focused on unifying different classes of energetic transients through mixing and breakout channels will find the parameter study and signatures useful. It deserves peer review because the methods are solid, the results are presented clearly, and the limitations are stated plainly.

Referee Report

2 major / 3 minor

Summary. The paper uses 2D hydrodynamics simulations to explore the effects of a long-lived central engine in core-collapse supernovae, varying the total energy, injection rate, and isotropy of energy deposition. Monte Carlo radiation transport post-processing is applied to the hydrodynamic results to derive observational signatures. The central claims are that sufficiently powerful engines excavate a central bubble that becomes Rayleigh-Taylor unstable, break through to accelerate and compositionally mix the entire ejecta, produce faster-rising optical light curves via enhanced photon escape, and yield spectra that evolve to resemble broad-line Ic supernovae, with possible narrow emission lines under certain conditions; variability in engine properties is suggested to explain a range of transients including FBOTs, broad-line Ic SNe, and SLSNe.

Significance. If the results hold, the work offers a useful parametric study of how central engines can reshape supernova ejecta dynamics and produce diverse observational classes. The combination of hydrodynamics with time-dependent Monte Carlo transport strengthens the link between dynamics and spectra/light curves, and the discussion of engine variability provides a framework for unifying multiple transient phenomena under a single mechanism.

major comments (2)

[Methods / simulation setup] The central engine is implemented as a prescribed, long-lived energy source whose total energy, injection rate, and isotropy are varied independently of the initial explosion (simulation setup and methods). This decoupling from self-consistent proto-neutron star, accretion, and neutrino/magnetic feedback is load-bearing for the claim that 'sufficiently powerful' engines produce global mixing and the observed spectral evolution, because it is unclear whether the explored parameter combinations are realizable in nature.
[Results / dynamical impact] All results are obtained in 2D axisymmetric hydrodynamics. The Rayleigh-Taylor instability, bubble breakout at distinct rupture points, and complete shredding/mixing of the ejecta (results on bubble evolution and outflow) may be quantitatively altered in 3D, where turbulent mixing and angular momentum transport differ; this affects the robustness of the faster light-curve rise and broad-line Ic spectral resemblance.

minor comments (3)

[Figures] Figure captions and axis labels should explicitly state the engine parameters (energy, rate, isotropy) for each model shown to allow direct comparison with the text.
[Radiation transport section] The Monte Carlo post-processing assumes LTE or specific opacity treatments; a brief statement on the validity of these approximations at the epochs shown would improve clarity.
[Discussion] A short comparison table or paragraph contrasting the 2D results with existing 3D central-engine or magnetar-driven simulations would help readers assess dimensionality effects.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive review and positive assessment of the significance of our work. We address each major comment point by point below, indicating planned revisions to strengthen the manuscript.

read point-by-point responses

Referee: [Methods / simulation setup] The central engine is implemented as a prescribed, long-lived energy source whose total energy, injection rate, and isotropy are varied independently of the initial explosion (simulation setup and methods). This decoupling from self-consistent proto-neutron star, accretion, and neutrino/magnetic feedback is load-bearing for the claim that 'sufficiently powerful' engines produce global mixing and the observed spectral evolution, because it is unclear whether the explored parameter combinations are realizable in nature.

Authors: We acknowledge that the parameterized central engine is decoupled from self-consistent proto-neutron star evolution, accretion, and neutrino or magnetic feedback. This is an intentional choice to enable a controlled parametric exploration of energy deposition effects. We will revise the methods and discussion sections to more explicitly state this assumption and to cite recent theoretical work on magnetar spin-down and fallback accretion that can produce comparable energy reservoirs and injection rates, thereby addressing the question of physical realizability within the context of a parametric study. revision: partial
Referee: [Results / dynamical impact] All results are obtained in 2D axisymmetric hydrodynamics. The Rayleigh-Taylor instability, bubble breakout at distinct rupture points, and complete shredding/mixing of the ejecta (results on bubble evolution and outflow) may be quantitatively altered in 3D, where turbulent mixing and angular momentum transport differ; this affects the robustness of the faster light-curve rise and broad-line Ic spectral resemblance.

Authors: We agree that three-dimensional effects could alter the quantitative details of Rayleigh-Taylor growth, breakout locations, and mixing efficiency due to differences in turbulence and angular momentum transport. We will add a dedicated paragraph to the discussion section acknowledging the 2D limitation, referencing literature on 2D versus 3D supernova simulations that shows persistence of key qualitative features such as bubble formation and enhanced mixing, and noting that while precise mixing fractions may vary, the overall dynamical trends and their impact on light curves and spectra are expected to remain robust. revision: partial

Circularity Check

0 steps flagged

No significant circularity in hydrodynamics and radiation transport results

full rationale

The paper derives its claims from two-dimensional hydrodynamics simulations of a prescribed central energy source (with varied total energy, injection rate, and isotropy) followed by time-dependent Monte Carlo radiation transport post-processing. Outcomes such as central bubble formation, Rayleigh-Taylor instability, ejecta acceleration and mixing for strong engines, faster-rising light curves, and spectral evolution to broad-line Ic features are direct numerical results of integrating the hydrodynamic equations and solving the radiation transport under the stated initial conditions and energy deposition prescriptions. No fitted parameters are redefined as predictions, no self-citations establish load-bearing uniqueness theorems, and no ansatz or renaming reduces the central results to the inputs by construction. The model is explicitly exploratory of independent engine parameters decoupled from collapse physics, making the derivation self-contained against the numerical methods and external benchmarks.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The study rests on standard hydrodynamics and radiation transport plus a parameterized central engine; no new particles or forces are introduced.

free parameters (2)

engine energy reservoir and injection rate
Varied parametrically to explore outcomes; values chosen to span observed transient classes.
degree of isotropy of energy deposition
Treated as a free parameter controlling bubble symmetry and breakout.

axioms (2)

domain assumption Two-dimensional axisymmetric hydrodynamics sufficiently captures the dominant Rayleigh-Taylor and breakout dynamics.
Invoked by choice of simulation dimensionality in the methods section implied by the abstract.
domain assumption Monte Carlo radiation transport with the adopted opacity treatment yields reliable observational signatures.
Post-processing step described in the abstract.

pith-pipeline@v0.9.0 · 5821 in / 1392 out tokens · 26089 ms · 2026-05-18T07:06:40.845292+00:00 · methodology

discussion (0)

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IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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the hydrodynamical evolution is mainly characterized by the ratio Ẽ_eng = E_eng / E_kin,ej

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

Magnetar Engines in Broad-lined Type Ic Supernovae and a Unified Picture for Magnetar-powered Stripped-envelope Supernovae
astro-ph.HE 2026-04 unverdicted novelty 6.0

Broad-lined Type Ic supernovae are powered by magnetar engines, showing a universal ejecta-mass versus initial-spin correlation across stripped-envelope supernova types that supports a common progenitor framework.