Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. II: Lightcurve Analysis

Anjasha Gangopadhyay; Avery Wold; Avinash Singh; Christoffer Fremling; Daichi Tsuna; Daniel A. Perley; Eric C. Bellm; Evan P. O'Connor; Jesper Sollerman; Josiah Purdum

arxiv: 2506.20068 · v2 · pith:23AC3F2Nnew · submitted 2025-06-25 · 🌌 astro-ph.HE · astro-ph.GA· astro-ph.SR

Low-Luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. II: Lightcurve Analysis

Kaustav K. Das , Mansi M. Kasliwal , Jesper Sollerman , Christoffer Fremling , Takashi J. Moriya , K-Ryan Hinds , Daniel A. Perley , Eric C. Bellm

show 13 more authors

Tracy X. Chen Evan P. O'Connor Michael W. Coughlin W. V. Jacobson-Galan Anjasha Gangopadhyay Matthew Graham S. R. Kulkarni Josiah Purdum Nikhil Sarin Steve Schulze Avinash Singh Daichi Tsuna Avery Wold

This is my paper

Pith reviewed 2026-05-22 01:18 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.GAastro-ph.SR

keywords Type IIP supernovaelow-luminosity supernovaelightcurve analysiscore-collapseprogenitor massexplosion energynickel massZwicky Transient Facility

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The pith

Low-luminosity Type IIP supernovae originate from core-collapse progenitors below 11 solar masses.

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

The paper studies light curves of 129 Type IIP supernovae from a local survey, including 16 low-luminosity ones. Using model fits, it shows that these faint events have distinctly low explosion energies, nickel masses, and ejecta masses. This supports the idea that they come from the lowest mass stars that undergo core collapse, with initial masses under 11 times the Sun's. Readers might care as this fills in the faint end of the supernova population and links brightness to progenitor properties. It also highlights possible differences in how these events evolve compared to brighter counterparts.

Core claim

LLIIP SNe represent the faint, low-energy end of the Type IIP population and originate from the lowest-mass core-collapse progenitors with ZAMS masses below 11 M⊙. Radiation-hydrodynamical fitting gives them nickel masses of 0.001-0.025 M⊙, explosion energies 0.1-0.28 × 10^51 erg, ejecta masses 8.1 M⊙, while the full sample reaches up to 0.222 M⊙ nickel, 4.43 × 10^51 erg energy, 24.8 M⊙ ejecta, and 16.7 M⊙ ZAMS masses. Strong correlations link peak brightness to energy and nickel mass even at the low end.

What carries the argument

Semi-analytical and radiation-hydrodynamical modeling of supernova light curves to determine explosion parameters and progenitor masses.

If this is right

Plateau slopes are often positive for LLIIP SNe, unlike brighter events, pointing to smaller progenitor radii and different density profiles.
The plateau duration depends only weakly on peak brightness, which may indicate that binary interactions influence the light curve shapes.
Explosion energy and nickel mass correlate strongly with peak brightness throughout the Type IIP population.
LLIIP events have the lowest values for all derived parameters, placing them at the faint end of a continuous distribution.

Where Pith is reading between the lines

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

This suggests a lower limit around 9-11 solar masses for the stars that produce observable core-collapse supernovae.
Events with extremely low nickel mass could represent a class of failed or electron-capture supernovae.
These results may help refine models of stellar evolution and the supernova contribution to galactic chemical enrichment.
Future direct progenitor detections could validate or refute the light-curve derived mass estimates.

Load-bearing premise

The radiation-hydrodynamical and semi-analytical models accurately recover the true explosion energies, ejecta masses, nickel masses, and ZAMS masses without large systematic biases from model assumptions or data selection.

What would settle it

Observing a low-luminosity Type IIP supernova whose progenitor star has a mass greater than 11 solar masses in pre-explosion archival images would falsify the claim that they originate from progenitors below 11 solar masses.

read the original abstract

The Zwicky Transient Facility Census of the Local Universe survey yielded a sample of 330 Type IIP supernovae (SNe) with well-constrained peak luminosities. In paper I (arXiv:2502.19493), we measured their luminosity function and volumetric rate. Here (paper II), we present the largest systematic study of lightcurve properties for Type IIP SNe from a volume-limited survey, analyzing a selected subset of 129 events, including 16 low-luminosity Type IIP (LLIIP) SNe with M${r,peak} \geq -16$ mag. We find that plateau slope correlates with peak brightness, with many LLIIP SNe showing positive slopes--suggesting smaller progenitor radii and distinct density profiles compared to brighter Type IIP SNe. The plateau duration shows only a weak dependence on peak brightness, likely suggesting binary interaction. One SN exhibits a plateau-to-tail drop of >3.5 mag, consistent with an electron-capture or failed SN with very low or zero nickel mass. We derive explosion and progenitor parameters of the entire Type IIP SN sample using semi-analytical and radiation-hydrodynamical models. Based on radiation-hydrodynamical model fitting, LLIIP SNe are characterized by low nickel masses (0.001-0.025 $\mathrm{M_\odot}$), low explosion energies (0.1-0.28 $\times 10^{51}$ erg), low ejecta masses ($8.1^{+0.8}_{-1.7}$ $\mathrm{M\odot}$), and ZAMS masses below 11 $\mathrm{M_\odot}$. In comparison, the full Type IIP SN sample spans a wider range with nickel masses (0.001-0.222 $\mathrm{M_\odot}$), explosion energies (0.10-4.43 $\times 10^{51}$ erg), ejecta masses (5.4-24.8 $\mathrm{M_\odot}$), and ZAMS masses (9.3-16.7 $\mathrm{M_\odot}$). We find strong correlations between peak brightness, explosion energy, and nickel mass that extend to the low-luminosity end. We conclude that LLIIP SNe represent the faint, low-energy end of the Type IIP population and originate from the lowest-mass core-collapse progenitors.

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 ZTF paper gives the largest volume-limited Type IIP lightcurve sample so far and extends the brightness-energy-nickel correlations into the faint regime, but the claim that LLIIP events come from ZAMS masses below 11 solar masses rests on radiation-hydro fits whose accuracy for low-energy cases is not yet clearly demonstrated.

read the letter

The main takeaway is that they have put together a clean sample of 129 Type IIP events from a volume-limited ZTF survey, with 16 falling into the low-luminosity category, and they show that plateau slope tracks peak brightness while duration does not. Many of the faint ones have positive slopes, which they link to smaller radii or different density profiles, and they flag one object with a steep drop to the tail as possibly an electron-capture or failed supernova. The modeling then returns low nickel masses, energies around 0.1-0.28 times 10^51 erg, and ejecta masses near 8 solar masses for the LLIIP group, leading to the ZAMS mass upper limit below 11 solar masses. That sample size and the extension of the trends are the concrete additions here. The observational trends are presented clearly enough to be useful for population work. The soft spots sit in the modeling step. The derived parameters come from fitting the same lightcurves that define the peak and slope measurements, so the reported correlations carry some built-in dependence on the model assumptions. The paper mentions binary interaction to explain the weak plateau-duration trend, yet the mass estimates appear to rely on single-star radiation-hydro models; that tension is not obviously resolved and could shift the ZAMS values. Details on priors, degeneracy checks, and how well the models perform when the plateau is flat or rising are not visible in the abstract, and the low-luminosity regime is exactly where those issues matter most. This work is aimed at people who track supernova demographics and progenitor constraints. Observers or modelers who need a larger, volume-limited reference set for faint Type IIP events will get something out of the trends and parameter ranges. It is worth sending to a serious referee because the sample itself is a step forward and the modeling claims can be tested and tightened in review.

Referee Report

3 major / 2 minor

Summary. The paper analyzes lightcurve properties of 129 Type IIP supernovae from a volume-limited ZTF sample (including 16 LLIIP events with M_r,peak ≥ -16 mag). It reports that plateau slope correlates with peak brightness (with many LLIIP showing positive slopes), plateau duration has only weak dependence on peak brightness, and derives explosion parameters via semi-analytical and radiation-hydrodynamical model fits. The central claim is that LLIIP SNe are the faint, low-energy end of the Type IIP population originating from the lowest-mass core-collapse progenitors with ZAMS masses below 11 M⊙, based on fitted values of low nickel mass (0.001-0.025 M⊙), low explosion energy (0.1-0.28 × 10^51 erg), and low ejecta mass (8.1^{+0.8}_{-1.7} M⊙).

Significance. If the radiation-hydrodynamical fits are shown to be unbiased in the low-energy regime, the work would strengthen constraints on the lower mass threshold for core-collapse events and the diversity of Type IIP progenitors, leveraging the largest volume-limited sample to date. The observational trends in plateau slope and the identification of one event with a >3.5 mag drop to the tail are useful additions to the literature on faint supernovae.

major comments (3)

[Radiation-hydrodynamical model fitting section] The inference of ZAMS masses below 11 M⊙ for the 16 LLIIP events rests on radiation-hydrodynamical fits that convert ejecta masses of ~8 M⊙ into progenitor masses. The manuscript does not present validation tests (e.g., recovery of injected parameters in mock lightcurves) for systematic biases arising from assumptions on density profiles, nickel mixing, or progenitor radius in the low-explosion-energy (0.1-0.28 × 10^51 erg) and low-nickel regime; without such tests the central progenitor-mass claim cannot be considered robust.
[Discussion of plateau-duration trends and progenitor modeling] The text invokes binary interaction to account for the observed weak dependence of plateau duration on peak brightness, yet the ZAMS-mass derivation from ejecta mass appears to rely on single-star evolutionary tracks. This mismatch is load-bearing for the <11 M⊙ conclusion and requires explicit quantification of how binary effects would alter the inferred ZAMS range.
[Parameter derivation and correlation analysis] Correlations between peak brightness, explosion energy, and nickel mass are obtained by fitting the same lightcurve data that were used to measure the peak magnitude and plateau properties. The manuscript should include mock-data experiments to assess the degree of circularity introduced by this procedure and its impact on the reported trends extending to the low-luminosity end.

minor comments (2)

[Abstract] The abstract provides no information on the fitting procedure, choice of priors, error propagation, or degeneracy checks; these details should be summarized even at the abstract level for a modeling-heavy paper.
[Figures] Figure captions for the lightcurve fits and parameter distributions would benefit from explicit statements of the model assumptions and the number of events shown.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their thorough and constructive review of our manuscript. The comments identify key areas where additional validation and clarification will improve the robustness of our conclusions on LLIIP progenitors. We address each major comment below and will incorporate the necessary revisions.

read point-by-point responses

Referee: [Radiation-hydrodynamical model fitting section] The inference of ZAMS masses below 11 M⊙ for the 16 LLIIP events rests on radiation-hydrodynamical fits that convert ejecta masses of ~8 M⊙ into progenitor masses. The manuscript does not present validation tests (e.g., recovery of injected parameters in mock lightcurves) for systematic biases arising from assumptions on density profiles, nickel mixing, or progenitor radius in the low-explosion-energy (0.1-0.28 × 10^51 erg) and low-nickel regime; without such tests the central progenitor-mass claim cannot be considered robust.

Authors: We agree that the current manuscript lacks explicit validation tests for the radiation-hydrodynamical fits in the low-energy, low-nickel regime, and that this limits the strength of the ZAMS mass claim. In the revised version we will add recovery tests: we will generate mock lightcurves using the same modeling code with injected parameters spanning our LLIIP range (E = 0.1–0.28 × 10^51 erg, M_Ni = 0.001–0.025 M⊙, M_ej ≈ 8 M⊙), incorporate realistic noise and sampling, and attempt to recover the inputs while varying density-profile assumptions, nickel mixing, and progenitor radius. The results will quantify any systematic offsets and will be presented in a new subsection. We note that the models are standard in the literature, but accept that regime-specific tests are required for robustness. revision: yes
Referee: [Discussion of plateau-duration trends and progenitor modeling] The text invokes binary interaction to account for the observed weak dependence of plateau duration on peak brightness, yet the ZAMS-mass derivation from ejecta mass appears to rely on single-star evolutionary tracks. This mismatch is load-bearing for the <11 M⊙ conclusion and requires explicit quantification of how binary effects would alter the inferred ZAMS range.

Authors: The referee correctly notes the tension between our invocation of binary interaction for the plateau-duration trend and our use of single-star tracks to map ejecta mass to ZAMS mass. In the revision we will add an explicit quantification: referencing binary population-synthesis results, we estimate that envelope stripping in the 8–11 M⊙ range can reduce ejecta mass by 1–3 M⊙ relative to single-star models. This implies that our measured M_ej ≈ 8.1 M⊙ could correspond to ZAMS masses up to ~12 M⊙ in the most extreme binary cases. Even after this adjustment the bulk of the LLIIP sample remains below 12 M⊙, supporting the conclusion that these events trace the lowest-mass core-collapse progenitors. The revised discussion will present this range and its effect on the <11 M⊙ statement. revision: yes
Referee: [Parameter derivation and correlation analysis] Correlations between peak brightness, explosion energy, and nickel mass are obtained by fitting the same lightcurve data that were used to measure the peak magnitude and plateau properties. The manuscript should include mock-data experiments to assess the degree of circularity introduced by this procedure and its impact on the reported trends extending to the low-luminosity end.

Authors: We acknowledge that deriving correlations from model fits to the identical lightcurve data used for direct measurements can introduce circularity. To evaluate its impact we will perform mock-data experiments in the revised manuscript. We will generate a grid of synthetic lightcurves with known input peak magnitudes, explosion energies, and nickel masses (including the LLIIP regime), add realistic photometric errors and cadence, measure the apparent peak and plateau properties, then apply our fitting pipeline and compare recovered versus input correlations. Special attention will be given to whether the low-luminosity trends are preserved or biased. The outcome of these tests will be reported to demonstrate that the observed correlations are not artifacts of the analysis. revision: yes

Circularity Check

1 steps flagged

Correlations between peak brightness and fitted explosion/Ni parameters are partly tautological with the lightcurve fitting process

specific steps

fitted input called prediction [Abstract; lightcurve analysis and model-fitting results]
"We find strong correlations between peak brightness, explosion energy, and nickel mass that extend to the low-luminosity end. [...] Based on radiation-hydrodynamical model fitting, LLIIP SNe are characterized by low nickel masses (0.001-0.025 M⊙), low explosion energies (0.1-0.28 × 10^{51} erg), low ejecta masses (8.1^{+0.8}_{-1.7} M⊙), and ZAMS masses below 11 M⊙."

Peak brightness is an observed input measured from the lightcurves. Explosion energy, nickel mass and ejecta mass are outputs of fitting models to those identical lightcurves. The correlations and the LLIIP characterization are therefore partly forced by construction: the fitting procedure is constrained to reproduce the observed peak and shape, so the reported relations between brightness and fitted parameters are not independent results but include a tautological component.

full rationale

The paper measures peak brightness and plateau properties directly from the observed lightcurves of 129 Type IIP events (including 16 LLIIP). It then fits semi-analytical and radiation-hydrodynamical models to those same lightcurves to extract explosion energy, nickel mass, ejecta mass, and ZAMS mass. The reported strong correlations between peak brightness and the fitted energy/Ni values, plus the characterization of LLIIP SNe as low-energy/low-Ni/low-mass, therefore contain a component enforced by the fitting procedure rather than constituting fully independent predictions. The central ZAMS <11 M⊙ claim rests on these fits plus a standard ejecta-to-ZAMS mapping; while the mapping itself is not circular, the input parameters to the mapping are. No self-citation load-bearing chain or self-definitional equation is present. This yields partial circularity (score 6) but leaves independent physical content in the model assumptions.

Axiom & Free-Parameter Ledger

3 free parameters · 1 axioms · 0 invented entities

Central conclusions rest on the validity of radiation-hydrodynamical model fits that introduce multiple fitted physical quantities and assume the models capture the dominant physics without large systematic offsets.

free parameters (3)

nickel mass = 0.001-0.025 M⊙ for LLIIP
Fitted to reproduce observed peak brightness and tail luminosity in the lightcurve models.
explosion energy = 0.1-0.28 × 10^51 erg for LLIIP
Fitted parameter in radiation-hydrodynamical models to match lightcurve shape and duration.
ejecta mass = 8.1+0.8-1.7 M⊙ for LLIIP
Derived from model fits to plateau duration and velocity indicators.

axioms (1)

domain assumption Semi-analytical and radiation-hydrodynamical models accurately map observed lightcurve properties to physical explosion parameters without significant systematic bias.
Invoked when converting fitted lightcurve parameters into progenitor ZAMS masses and explosion energies.

pith-pipeline@v0.9.0 · 6106 in / 1451 out tokens · 48807 ms · 2026-05-22T01:18:07.637197+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

We derive explosion and progenitor parameters of the entire Type IIP SN sample using semi-analytical and radiation-hydrodynamical models... Based on radiation-hydrodynamical model fitting, LLIIP SNe are characterized by low nickel masses (0.001-0.025 M⊙), low explosion energies (0.1-0.28 × 10^51 erg), low ejecta masses (8.1+0.8-1.7 M⊙), and ZAMS masses below 11 M⊙.
IndisputableMonolith/Foundation/DimensionForcing.lean alexander_duality_circle_linking unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

We use this model grid to measure the explosion parameters... progenitor masses (9, 10, 12, 14, 16, and 18 M⊙ at the zero-age main sequence (ZAMS), solar metallicity), explosion energies (0.5, 1.0, ... 5.0 × 10^51 erg)

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extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
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contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
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