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REVIEW 1 major objections 3 references

SN 2018erx is explained as interaction between low-mass ejecta and a compact 0.3-solar-mass carbon-rich shell at 0.7 AU from an ultra-stripped core-collapse event.

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2026-06-30 00:19 UTC pith:AZ7EPQVN

load-bearing objection SN 2018erx adds a well-observed fast Icn event with quantified compact CSM and dust excess, but the ultra-stripped low-ejecta conclusion rests on semi-analytical assumptions that are not fully tested. the 1 major comments →

arxiv 2605.24811 v1 pith:AZ7EPQVN submitted 2026-05-24 astro-ph.HE astro-ph.SR

SN~2018erx: A fast-evolving, dust-reddened Type Icn supernova with broad C II emission lines

Kaustav K. Das , Anjasha Gangopadhyay , Mansi M. Kasliwal , Jesper Sollerman , Daniel A. Perley , Steve Schulze , Christoffer Fremling , Michael W. Coughlin
show 12 more authors
Kishalay De Avishay Gal-Yam Ariel Goobar Matthew Graham Frank J. Masci Takashi J. Moriya Josiah Purdum Sam Rose Ben Rusholme Nikhil Sarin Roger Smith Daichi Tsuna
This is my paper
classification astro-ph.HE astro-ph.SR
keywords Type Icn supernovacore-collapse supernovacircumstellar materialultra-stripped supernovadust reddeningSN 2018erxZTF
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 paper reports the discovery of SN 2018erx, a supernova that rises to peak in just over two days and declines in three, with broad carbon emission lines indicating interaction with carbon-rich material. Semi-analytical modeling of the light curve and spectra yields a low ejecta mass of 0.11 solar masses, a compact circumstellar shell of 0.3 solar masses at 0.7 AU, and very little radioactive nickel. An infrared excess at later times is attributed to pre-existing dust, implying multiple episodes of mass loss in the years before explosion. These features together favor an ultra-stripped explosion of a low-mass helium star in a binary system.

Core claim

SN 2018erx is a fast-evolving, dust-reddened Type Icn supernova whose photometry and spectra are explained by interaction with a compact carbon-rich CSM shell of mass ~0.3 solar masses at ~0.7 AU, low ejecta mass ~0.11 solar masses, and nickel yield ≲ 5e-3 solar masses, pointing to an ultra-stripped core-collapse event from a low-mass He star in a binary.

What carries the argument

Semi-analytical CSM-interaction modeling that fits the rapid light curve and carbon line widths to derive shell mass, radius, and ejecta mass.

Load-bearing premise

The semi-analytical CSM-interaction model accurately captures the physical conditions without significant contributions from other energy sources or geometry effects.

What would settle it

A measurement of significantly higher nickel mass or a light curve that deviates from the interaction model predictions in multi-band or spectroscopic follow-up would falsify the derived parameters.

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

If this is right

  • The progenitor experienced enhanced pre-supernova mass loss forming a dense inner shell and an earlier episode producing an outer dusty layer 10-200 years prior.
  • The low ejecta mass and nickel yield place the event at the extreme low end of hydrogen-poor supernovae.
  • Dust-enshrouded explosions of this type may be missed by optical surveys and require infrared searches.
  • The carbon-rich emission and overall properties support a multi-component circumstellar environment around the exploding star.

Where Pith is reading between the lines

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

  • Similar events could be used to calibrate the fraction of stripped-envelope supernovae that arise from binary mass transfer rather than single-star winds.
  • If the compact shell is common, radio or X-ray observations of future analogs might directly measure the shell density profile.
  • The short time between mass-loss episodes constrains the final evolutionary stages of low-mass helium stars in binaries.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

1 major / 0 minor

Summary. The manuscript reports the discovery and characterization of SN 2018erx (ZTF18abkmbpy), classified as a fast-evolving Type Icn supernova on the basis of broad C II emission lines with widths ~3800 km/s. Photometry shows a rapid rise from half-maximum to peak in 2.1 d and decline in 3.1 d. Semi-analytical CSM-interaction modeling is used to infer a compact carbon-rich shell with M_CSM ≈ 0.3 M_⊙ at R_0 ≈ 0.7 AU, low ejecta mass M_ej ≈ 0.11 M_⊙, and M_Ni ≲ (3–5)×10^{-3} M_⊙. A NIR excess at +29 d is attributed to pre-existing circumstellar dust (M_d ~10^{-6}–10^{-5} M_⊙). The authors interpret the multi-component CSM and low masses as evidence for an ultra-stripped core-collapse event from a low-mass He star in a binary system.

Significance. If the modeling is robust, the result is significant for the study of stripped-envelope supernovae: it supplies a rare, well-observed Icn event with quantitative constraints on both an inner dense interaction shell and an outer dusty layer, thereby tracing multi-episode pre-SN mass loss on timescales of 10–200 yr. The placement at the low end of the H-poor mass distribution and the suggestion of selection biases against dust-reddened events in optical surveys are useful for binary-evolution and progenitor models. The work adds concrete observational anchors to the ultra-stripped scenario.

major comments (1)
  1. [modeling section] Modeling section (abstract and associated paragraph): the central claim that the rapid light curve is produced by ejecta interaction with a compact spherical shell yielding M_CSM ≈ 0.3 M_⊙, R_0 ≈ 0.7 AU and M_ej ≈ 0.11 M_⊙ rests on the semi-analytical fit. The manuscript provides neither the model equations, the photometric data table with uncertainties, the fitting procedure, χ² values, nor tests for deviations from spherical symmetry or additional energy sources (radioactive heating is only given as an upper limit). This directly affects whether the low ejecta mass and ultra-stripped interpretation are uniquely constrained, consistent with the stress-test concern.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful and constructive review. We address the single major comment below and will revise the manuscript to incorporate the requested details on the modeling.

read point-by-point responses

  1. Referee: [modeling section] Modeling section (abstract and associated paragraph): the central claim that the rapid light curve is produced by ejecta interaction with a compact spherical shell yielding M_CSM ≈ 0.3 M_⊙, R_0 ≈ 0.7 AU and M_ej ≈ 0.11 M_⊙ rests on the semi-analytical fit. The manuscript provides neither the model equations, the photometric data table with uncertainties, the fitting procedure, χ² values, nor tests for deviations from spherical symmetry or additional energy sources (radioactive heating is only given as an upper limit). This directly affects whether the low ejecta mass and ultra-stripped interpretation are uniquely constrained, consistent with the stress-test concern.

    Authors: We agree that the current presentation of the modeling lacks sufficient detail. In the revised manuscript we will: (1) reproduce the key equations of the semi-analytical CSM-interaction model with appropriate citations, (2) add a table of the photometric data points including uncertainties, (3) describe the χ²-minimization fitting procedure and report the best-fit χ² values, and (4) explicitly discuss the assumptions of spherical symmetry, the treatment of radioactive heating as an upper limit, and the possible impact of deviations from these assumptions on the derived M_ej, M_CSM and M_Ni. These additions will clarify the robustness of the ultra-stripped interpretation. revision: yes

Circularity Check

0 steps flagged

No significant circularity in observational classification or semi-analytical modeling

full rationale

The paper reports photometric and spectroscopic observations of SN 2018erx, classifies it as Type Icn based on broad C II lines, and applies semi-analytical CSM-interaction modeling to fit parameters (M_CSM ≈ 0.3 M_⊙, R0 ≈ 0.7 AU, M_ej ≈ 0.11 M_⊙) to the light curve and spectra. No equations are presented that reduce these fitted quantities to inputs by definition, nor are any 'predictions' shown that are statistically forced by the same data subset. No self-citations are invoked as load-bearing uniqueness theorems or ansatzes. The derivation chain is self-contained against external benchmarks (observed rise/decline times, line widths, NIR excess) and does not exhibit any of the enumerated circular patterns.

Axiom & Free-Parameter Ledger

4 free parameters · 0 axioms · 0 invented entities

Only abstract available; modeling parameters are presented as fitted results rather than free parameters chosen by hand, but the semi-analytical framework itself rests on standard assumptions not detailed here.

free parameters (4)
  • M_CSM = ~0.3 M_sun
    Value ~0.3 solar masses obtained from semi-analytical CSM-interaction modeling of the light curve.
  • R0 = ~0.7 AU
    Initial radius ~0.7 AU from the same modeling.
  • M_ej = ~0.11 M_sun
    Ejecta mass ~0.11 solar masses from modeling.
  • M_Ni = ≲ 5×10^{-3} M_sun
    Upper limit ≲ (3-5)×10^{-3} solar masses from radioactive yield constraints.

pith-pipeline@v0.9.1-grok · 6029 in / 1368 out tokens · 37957 ms · 2026-06-30T00:19:40.565869+00:00 · methodology

0 comments
read the original abstract

We present the discovery and characterization of SN~2018erx (ZTF18abkmbpy), a fast-evolving, unusually red, interacting stripped-envelope supernova. Spectroscopically, SN~2018erx shows broad \ion{C}{2} emission with characteristic widths of $\sim\!3800$~km~s$^{-1}$, consistent with interaction with carbon-rich circumstellar material and a Type~Icn core-collapse SN classification. Photometrically, it evolves rapidly, rising from half-maximum to peak in 2.1~d and declining back in 3.1~d. Semi-analytical CSM-interaction modeling favors a compact, shell-like CSM with $M_{\rm CSM}\approx0.3\,M_\odot$, $R_0\approx0.7$~AU, and a low ejecta mass of $M_{\rm ej}\approx0.11\,M_\odot$. The radioactive yield is also small, with $M_{\rm Ni}\lesssim(3$--$5)\times10^{-3}\,M_\odot$, placing SN~2018erx at the low end of the H-poor distribution. At +29~d after peak, we detect a near-infrared excess consistent with pre-existing local circumstellar dust, with $M_{\rm d}\sim10^{-6}$--$10^{-5}\,M_\odot$. Together, the rapid evolution, strong local reddening, carbon-rich emission, and dust point to a multi-component circumstellar environment: a dense inner interaction region from enhanced pre-SN mass loss and an outer dusty layer from an earlier mass-loss episode roughly $10$--$200$~yr before core collapse. These properties favor an ultra-stripped core-collapse explosion of a low-mass He star in a binary system, with fallback-modified Wolf--Rayet collapse or merger-driven mass loss remaining possible alternatives. SN~2018erx provides rare insight into the mass-loss history of stripped-envelope SNe and suggests that dust-enshrouded explosions of this kind may be underrepresented in optical surveys.

Figures

Figures reproduced from arXiv: 2605.24811 by Anjasha Gangopadhyay, Ariel Goobar, Avishay Gal-Yam, Ben Rusholme, Christoffer Fremling, Daichi Tsuna, Daniel A. Perley, Frank J. Masci, Jesper Sollerman, Josiah Purdum, Kaustav K. Das, Kishalay De, Mansi M. Kasliwal, Matthew Graham, Michael W. Coughlin, Nikhil Sarin, Roger Smith, Sam Rose, Steve Schulze, Takashi J. Moriya.

Figure 1
Figure 1. Figure 1: Multi-band optical and near-infrared lightcurves of SN 2018erx. The left axis shows the observed apparent magni￾tudes, while the right axis indicates the corresponding absolute magnitudes. Both axes are corrected for Milky Way extinction, but no correction for host or circumstellar dust extinction has been applied. The phase is given in rest-frame days relative to the epoch of r-band maximum. Downward tria… view at source ↗
Figure 2
Figure 2. Figure 2: Keck/LRIS spectrum of SN 2018erx obtained at a phase of +2.4 days (rest-frame) relative to r-band maximum. The grey line shows the original spectrum, while the black curve indicates a smoothed version. The purple shaded regions mark the wavelengths of prominent C II λλ4267, 5145, 5890, 6578, and 7236 emission lines [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Cumulative distribution functions (CDFs) of rise time (left) and decline time (right) for stripped-envelope SN subclasses from the ZTF Bright Transient Survey (BTS) sample, while the SNe Icn sample combines the BTS SNe Icn with SN 2019jc, SN 2021ckj, SN 2023qre, and SN 2023rau. The vertical dashed line indicates the measured values for SN 2018erx, showing that it lies among the most rapidly evolving events… view at source ↗
Figure 4
Figure 4. Figure 4: r-band absolute-magnitude lightcurve of SN 2018erx compared with rapidly evolving transients and SESNe from the literature. Red symbols show SN 2018erx assuming no host extinction (AV = 0), while purple symbols show the extinction￾corrected lightcurve adopting AV = 3.3 mag. For comparison, lightcurves of several fast transients and interacting SESNe (colored markers) and a broader sample of stripped-envelo… view at source ↗
Figure 5
Figure 5. Figure 5: Spectral evolution of SN 2018erx from −1.6 to +16.4 days relative to r-band maximum. The spectra are shown in the host-galaxy rest frame and have been vertically offset for clarity. The gray lines show the original spectra, while the black curves indicate smoothed versions. Indentifications of prominent lines are marked with dashed vertical lines, including C II, He I, N II, N III, O I, and Ca ii. C II emi… view at source ↗
Figure 6
Figure 6. Figure 6: Comparison of the +2.4 day Keck/LRIS spec￾trum of SN 2018erx (black) with representative spectra of Type Ibn (blue) and Type Icn (red) supernovae at phases of ∼ 3–10 days relative to peak. The spectra are shown in the rest frame and vertically offset for clarity. Dashed vertical lines mark the wavelengths of prominent spectral features, including C II, He I, He II, N II, N III, and Ca ii. 10 5 0 5 10 C II … view at source ↗
Figure 7
Figure 7. Figure 7: Velocity profiles of prominent C II emission lines in SN 2018erx compared with representative Type Icn supernovae. The panels show the regions around C II λ7236, λ6587, and λ5890. Spectra are plotted in velocity space rela￾tive to the rest wavelength of each transition. The spectrum of SN 2018erx (black) is compared with those of the Type Icn events SN 2022ann (red) and SN 2019hgp (blue). The simi￾lar line… view at source ↗
Figure 9
Figure 9. Figure 9: Multi-band light-curve fit of SN 2018erx using the CSM-interaction model implemented in redback. The observed photometry in the g, r, and i bands is shown as col￾ored points, while the solid curves represent the best-fitting model. The spectra of SN 2018erx show prominent intermediate-width C II emission and related inter￾action signatures (Figures 5 and 7), indicating that the line-forming region is assoc… view at source ↗
Figure 10
Figure 10. Figure 10: Corner plot showing the posterior distributions of the CSM-interaction model parameters obtained from the redback fit to the multi-band lightcurve of SN 2018erx. The diagonal panels show the marginalized posterior distributions, while the off-diagonal panels show the parameter covariances. The dashed lines indicate the median values and 1σ credible intervals. while the outer radius inferred from the best-… view at source ↗
Figure 11
Figure 11. Figure 11: Comparison of the circumstellar interaction parameters inferred for SN 2018erx with literature samples of Type Ibn/Icn SNe. Left: Inner CSM radius R0 versus CSM mass MCSM. The black star marks the values inferred for SN 2018erx from the redback interaction modeling, while blue and red symbols show literature estimates for SNe Ibn and SNe Icn, respectively. Right: Cumulative distribution functions (CDFs) o… view at source ↗
Figure 12
Figure 12. Figure 12: Comparison of the 56Ni mass (MNi) and ejecta mass (Mej) of SN 2018erx with SESNe from the literature. The red symbol marks SN 2018erx, while blue triangles denote Type Icn events (Pellegrino et al. 2022b). The arrow indicates that the inferred 56Ni mass is an upper limit. Gray symbols show literature measurements for other SESN subclasses from D24 (Das et al. 2023a), D23 (Das et al. 2023b), and T18 (Taddi… view at source ↗
Figure 13
Figure 13. Figure 13: Schematic illustration of the CSM environment inferred for SN 2018erx from the lightcurve and spectral modeling. The figure summarizes the compact C-rich inner CSM responsible for the rapid interaction, together with the more extended dusty component inferred from the strong extinction and late-time near-infrared excess. and high inner density (ρ0 ≈ 9.6 × 10−13 g cm−3 ) disfavor a steady WR wind and inste… view at source ↗

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Reference graph

Works this paper leans on

3 extracted references · 1 canonical work pages

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    The continuum-subtracted host spectrum used to measure the line fluxes

    After correction (A V = 3.3) (days) logL bb Tbb Rbb logL bb Tbb Rbb (erg s−1) (K) (R ⊙) (erg s −1) (K) (R ⊙) −3.3 41.96 +0.06 −0.06 3130+150 −140 52380+8650 −7650 42.72+0.12 −0.03 6840+2120 −730 26370+5530 −8720 −2.3 42.27 +0.03 −0.03 3900+100 −100 48180+4340 −3810 43.38+0.04 −0.03 9020+770 −610 32270+3560 −3550 −1.3 42.28 +0.01 −0.01 4340+60 −60 39350+15...

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    2018erx (Av = 3.3) 2006jc OGLE12-006 2010al iPTF14aki 2019uo 2019wep 2019hgp 2021ckj 2021csp 2023xgo Figure A2.Evolution of the optical color (g−r) for SN 2018erx compared with Type Ibn (blue symbols) and Type Icn (pink symbols) supernovae from the literature. Filled black circles show the observed colors of SN 2018erx assuming no host extinction (AV = 0)...

    2020