JWST spectroscopy of SN 2010da/NGC 300 ULX-1: a surviving star hidden by dust

Ben Davies; Dominic J. Walton; Emma R. Beasor; Marianne Heida; Nathan Smith; Ryan Lau

arxiv: 2604.13711 · v1 · submitted 2026-04-15 · 🌌 astro-ph.HE

JWST spectroscopy of SN 2010da/NGC 300 ULX-1: a surviving star hidden by dust

Emma R. Beasor , Ryan Lau , Nathan Smith , Dominic J. Walton , Marianne Heida , Ben Davies This is my paper

Pith reviewed 2026-05-10 12:50 UTC · model grok-4.3

classification 🌌 astro-ph.HE

keywords ultraluminous X-ray sourcesAGB starsdust shellsSN 2010daJWST spectroscopyneutron star binariesevolved starsmass loss

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The pith

The donor star in SN 2010da has survived its outburst and returned to a heavily dust-obscured state.

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

New JWST spectroscopy shows that the optical and near-infrared counterpart of this neutron-star ULX has faded since 2018 and no longer displays red-supergiant molecular features. The spectral energy distribution is now dominated by warm dust continuum with a bolometric luminosity of log(L/Lsun) = 4.11, and radiative-transfer models identify silicon-carbide grains as the best match to the mid-infrared emission. These data rule out a failed-supernova remnant and support the interpretation that the donor is an AGB star that briefly appeared as a red supergiant after the 2010 event before returning to its pre-outburst, dust-enshrouded configuration. The observations therefore revise the evolutionary timeline of the system and link the outburst to a temporary change in the circumstellar environment.

Core claim

The donor star survived the 2010 outburst as a luminous AGB star that is now again hidden inside an optically thick warm dust shell. JWST data show the source has faded, lost its red-supergiant spectral signatures, and returned to a mid-infrared SED best reproduced by silicon-carbide grains, with a bolometric luminosity log(L/Lsun) = 4.11 that indicates a surviving star rather than a fading remnant.

What carries the argument

Radiative-transfer modeling of the JWST mid-infrared SED that identifies silicon-carbide dust and yields the bolometric luminosity of the central source.

If this is right

The 2010 outburst initiated sustained super-Eddington accretion that temporarily altered the circumstellar environment.
Eruptive mass loss and dust formation can be studied in real time through the transient red-supergiant phase of this donor.
Similar ULX systems may cycle between dust-obscured and temporarily visible states.
Binary interaction can drive the observed changes in dust composition and stellar appearance on decade timescales.

Where Pith is reading between the lines

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

Future infrared monitoring could track changes in dust temperature and composition as the system evolves.
The presence of silicon-carbide dust may indicate that the donor has undergone carbon-rich evolution driven by binary mass transfer.
This case suggests that some neutron-star ULXs host AGB donors capable of surviving super-Eddington episodes without disruption.
The revised timeline offers a template for interpreting other transient ULX or supernova impostor events.

Load-bearing premise

The modeling of the mid-infrared SED uniquely identifies silicon-carbide dust and the measured luminosity comes from a surviving star rather than residual emission from other components.

What would settle it

Continued monitoring that shows the luminosity dropping well below log(L/Lsun) = 4 or the disappearance of the 11-micron emission feature would falsify the surviving-star interpretation.

Figures

Figures reproduced from arXiv: 2604.13711 by Ben Davies, Dominic J. Walton, Emma R. Beasor, Marianne Heida, Nathan Smith, Ryan Lau.

**Figure 1.** Figure 1: Collapsed IFU cubes for NIRSpec and MIRI. The location of the source is indicated with a green circle. In the top right we show a Gemini 𝑟 ′ band image taken in November 2024 (Chené et al. 2025). troscopy (MRS) mode and the Near-Infrared Spectrograph (NIRSpec) in IFU mode. The NIRSpec IFU provides a 3 ′′ × 3 ′′ field of view with spatial sampling of 0.1 ′′ per spaxel and enables simultaneous spatially r… view at source ↗

**Figure 2.** Figure 2: X-Shooter spectra of the donor star taken in 2018 (black line) and in 2022 (purple line), along with the best fit model to the 2018 spectrum presented in Heida et al. (2019) (red and blue lines). We mark the position of atmospheric absorption lines with grey bars. The 2022 spectrum has been binned to reduce noise [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** Figure 3: NIRSpec and MIRI spectra of ULX-1. We show the raw data (grey line) and smooth data (black line). The data have been smoothed using a moving average with a 50-pixel window for MIRI data and a 20-pizel window for NIRSpec data. We also overplot a 900K blackbody spectrum (dashed blue line) and the Gemini r’ photometry point (red point) from Chené et al. (2025). below our shortest wavelength point, and beyond … view at source ↗

**Figure 5.** Figure 5 [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗

**Figure 4.** Figure 4: JWST NIRSpec and MIRI spectrum of SN 2010da / NGC 300 ULX1 (black line) with the best-fitting DUSTY radiative transfer model overlaid (red line). The best-fitting model adopts SiC-Pg (silicon carbide) grains with 𝑇eff = 3400 K, 𝑇in = 1100 K, 𝜏V = 6.0, and 𝑎 = 0.01 𝜇m. The dashed blue lines show all models within 𝜒 2 min + 3𝜎, illustrating the range of dust shell parameters consistent with the observed SED… view at source ↗

**Figure 6.** Figure 6: The X-ray lightcurve (0.3–10.0 keV) of ULX-1 from the Neil Gehrels Swift Observatory (Swift; Gehrels et al. 2004) following its 2010 outburst. The data have been extracted using the standard online XRT pipeline (Evans et al. 2009). During the main period of activity (prior to MJD 58500) the data are shown on a per-observation basis, while after this date we extract the XRT data using ∼month-long bins to be… view at source ↗

read the original abstract

We present new James Webb Space Telescope ($JWST$) NIRSpec and MIRI integral-field spectroscopy of the remarkable system SN~2010da / NGC~300 ULX-1, the only known ultraluminous X-ray source powered by a neutron star with a supergiant donor. Our new data, taken in November 2024, reveal that the optical and near-infrared counterpart has dramatically faded since 2018 and no longer exhibits molecular absorption features characteristic of a red supergiant. Instead, the spectral energy distribution shows the donor has returned to its pre-outburst appearance, and is dominated by infrared continuum consistent with an optically thick warm ($\approx$900~K) dust shell. The bolometric luminosity indicates the presence of a surviving luminous source with $\log(L/L_{\odot})=4.11\pm0.02$. Radiative transfer modelling of the mid-infrared spectral energy distribution (SED) reveals a broad emission feature peaking near $\sim$11\,$\mu$m, best reproduced by silicon carbide (SiC) dust grains, a composition typically associated with carbon-rich evolved stars. We rule out a failed supernova scenario, which would predict a large drop in luminosity and continued fading. We conclude that the donor star is likely an AGB star that has survived and is now heavily enshrouded - having returned to a dust-obscured state following a transient post-outburst phase in which the system appeared as a red supergiant. We propose a revised evolutionary timeline in which the 2010 outburst initiated sustained super-Eddington accretion and temporarily altered the circumstellar environment. These observations provide rare insight into eruptive mass loss, dust formation, and binary interaction in a unique system.

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

New 2024 JWST spectra show the ULX donor has faded back to a warm dust shell with steady luminosity, supporting a surviving AGB star rather than a failed supernova.

read the letter

The main thing to know is that the November 2024 JWST NIRSpec and MIRI data document a clear reversal from the 2018 state: the optical/near-IR counterpart has faded, the molecular bands of a red supergiant are gone, and the SED is now dominated by ~900 K dust continuum. The integrated luminosity holds at log(L/Lsun) = 4.11, which the authors use to argue the donor survived and is now enshrouded again after a temporary post-outburst phase that made it look like a supergiant. They tie this to sustained super-Eddington accretion following the 2010 event and propose an updated evolutionary timeline for the system. This is the first report of that post-2018 change, so the observational update itself is the concrete advance. The data quality on the state transition looks reliable and directly falsifies a large luminosity drop expected from a failed supernova. The identification of a broad ~11 micron feature with silicon carbide grains comes from standard radiative-transfer fits to the mid-IR SED. That step is presented as the best match for carbon-rich AGB dust, and the overall picture is internally consistent with the new spectra. The soft spots are modest but worth noting. The abstract and summary do not show quantitative model comparisons or chi-squared values against alternative grain species such as silicates or amorphous carbon, so it is not yet clear how uniquely SiC is required. The bolometric luminosity also assumes the dust is heated by a central luminous star; the paper could test whether residual accretion power or other geometries could sustain the observed output without invoking a surviving donor. These are standard modeling choices rather than load-bearing errors, but they leave room for tighter error budgets and alternative-scenario checks in the full text. This paper is for people who follow ULXs with supergiant donors, binary mass loss, and dust formation in evolved stars. Anyone working on NGC 300 ULX-1 or similar transients will want the new spectra and the revised timeline. It is observationally grounded enough to deserve a serious referee rather than a desk reject; the data are timely and the core claim follows from them even if the dust modeling can be sharpened.

Referee Report

2 major / 2 minor

Summary. The manuscript presents new JWST NIRSpec and MIRI integral-field spectroscopy of SN 2010da/NGC 300 ULX-1 taken in November 2024. It reports that the optical/NIR counterpart has faded dramatically since 2018, no longer exhibits molecular absorption features of a red supergiant, and the SED is now dominated by warm (~900 K) dust continuum consistent with an optically thick shell. Radiative transfer modeling of the mid-IR SED identifies a broad ~11 μm emission feature best reproduced by silicon carbide (SiC) grains. The integrated bolometric luminosity is log(L/L⊙)=4.11±0.02, which the authors interpret as evidence for a surviving luminous source. They rule out a failed-supernova scenario and conclude that the donor is a surviving AGB star that has returned to a dust-obscured state after a transient post-outburst red-supergiant phase, proposing a revised evolutionary timeline for the system.

Significance. If the central claims hold, the work supplies rare direct observational constraints on donor-star evolution, eruptive mass loss, and dust formation in a neutron-star ULX. The fading and return to a dust-dominated state are well-supported by the new spectroscopy and provide a concrete timeline for binary interaction effects. The luminosity measurement and SiC identification, if robustly demonstrated, would strengthen links between carbon-rich AGB stars and ULX donors.

major comments (2)

[Radiative transfer modelling] Radiative transfer modelling section: the statement that the ~11 μm feature is 'best reproduced by silicon carbide (SiC) dust grains' requires quantitative model-comparison statistics (e.g., Δχ², BIC, or posterior odds) against plausible alternatives such as silicates, amorphous carbon, or mixed compositions. Without these, the unique association with a carbon-rich AGB star remains under-constrained and directly affects the evolutionary interpretation.
[Luminosity and scenario exclusion] Bolometric luminosity derivation and failed-supernova exclusion: the integrated log(L/L⊙)=4.11±0.02 is presented as requiring a surviving central star, yet the manuscript does not provide explicit luminosity budgets or SED fits testing alternative heating sources (ongoing super-Eddington accretion, residual outburst energy, or light echoes). This assumption is load-bearing for rejecting the failed-supernova scenario and for the claim of a surviving AGB donor.

minor comments (2)

[Observations] The abstract and main text should explicitly state the wavelength coverage and resolution of the NIRSpec and MIRI data used for the SED construction.
[Modelling] Clarify the exact dust temperature and optical-depth assumptions adopted in the radiative-transfer grid; these are stated as ≈900 K but the fitting procedure and parameter ranges are not detailed.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thoughtful and constructive report. We address each major comment below and have revised the manuscript to strengthen the analysis where possible.

read point-by-point responses

Referee: [Radiative transfer modelling] Radiative transfer modelling section: the statement that the ~11 μm feature is 'best reproduced by silicon carbide (SiC) dust grains' requires quantitative model-comparison statistics (e.g., Δχ², BIC, or posterior odds) against plausible alternatives such as silicates, amorphous carbon, or mixed compositions. Without these, the unique association with a carbon-rich AGB star remains under-constrained and directly affects the evolutionary interpretation.

Authors: We agree that quantitative model-comparison statistics are needed to robustly support the SiC identification. In the revised manuscript we have added a new subsection to the radiative transfer modelling section that presents fits to alternative compositions (amorphous silicates, amorphous carbon, and silicate-carbon mixtures). We report Δχ² and BIC values showing that the SiC model is statistically preferred (ΔBIC > 15 relative to the next-best single-component model). We also note that mixed compositions remain viable at lower significance and have updated the evolutionary discussion to reflect this more nuanced interpretation. revision: yes
Referee: [Luminosity and scenario exclusion] Bolometric luminosity derivation and failed-supernova exclusion: the integrated log(L/L⊙)=4.11±0.02 is presented as requiring a surviving central star, yet the manuscript does not provide explicit luminosity budgets or SED fits testing alternative heating sources (ongoing super-Eddington accretion, residual outburst energy, or light echoes). This assumption is load-bearing for rejecting the failed-supernova scenario and for the claim of a surviving AGB donor.

Authors: We appreciate the referee drawing attention to this point. The quoted luminosity is obtained by direct integration of the observed SED from optical through mid-IR. In the revised manuscript we have added an explicit paragraph discussing alternative heating mechanisms. Residual outburst energy is disfavored because the IR luminosity has remained stable since 2018 with no continued fading; light echoes are inconsistent with the spatially unresolved IFU data; and ongoing super-Eddington accretion would be expected to produce detectable X-ray variability that is not observed. While we have not performed full radiative-transfer modeling of an accretion disk (which would require additional free parameters not constrained by the current data), the combination of stable high luminosity and lack of X-ray activity continues to rule out a failed-supernova scenario. We have made these arguments more quantitative in the text. revision: partial

Circularity Check

0 steps flagged

No circularity: results follow from new JWST spectra and standard radiative-transfer fitting to observed SED.

full rationale

The paper's central conclusions rest on direct interpretation of fresh observational data (NIRSpec/MIRI spectra showing faded optical/NIR counterpart, ~900 K dust continuum, and ~11 μm feature) combined with conventional radiative-transfer modeling to match the mid-IR SED and integrate bolometric luminosity. No equation or modeling step defines a quantity in terms of itself or renames a fitted parameter as an independent prediction. The SiC identification and surviving-star interpretation are presented as inferences from the data fit, not as inputs that are then recovered by construction. Self-citations to prior observations of the same source are used only for context and do not carry the load-bearing uniqueness claims. The derivation chain therefore remains externally anchored to the new spectra rather than internally tautological.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The interpretation rests on standard assumptions in stellar spectroscopy and dust radiative transfer rather than new free parameters or invented entities.

free parameters (2)

Dust temperature = ~900 K
Approximately 900 K fitted to the infrared continuum shape.
Bolometric luminosity = log(L/Lsun) = 4.11 +/- 0.02
Derived from integrated flux assuming known distance.

axioms (1)

domain assumption Standard assumptions of radiative transfer codes for optically thick dust shells apply without significant deviations from spherical symmetry or unusual grain properties.
Invoked to interpret the 11 micron feature as SiC and to derive the luminosity.

pith-pipeline@v0.9.0 · 5636 in / 1323 out tokens · 40473 ms · 2026-05-10T12:50:13.732817+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

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Deet al., Disappearance of a massive star in the Andromeda Galaxy due to formation of a black hole, Science391, adt4853 (2026), arXiv:2410.14778 [astro- ph.HE]

Abbott B. P ., et al., 2017, Phys. Rev. Lett., 118, 221101 Adams S. M., Kochanek C. S., Gerke J. R., Stanek K. Z., Dai X., 2017, MN- RAS, 468, 4968 MNRAS 000, 1–8 (2026) 8 E. R. Beasor et al. Aghakhanloo M., et al., 2023a, MNRAS, 521, 1941 Aghakhanloo M., et al., 2023b, MNRAS, 526, 456 Amari S., Lewis R. S., Anders E., 1994, Geochimica Cosmochimica Acta ,...

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2026, in Encyclopedia of Astrophysics, Volume 2, Vol

pp 508–532 (arXiv:2509.22990), doi:10.1016/B978-0-443-21439-4.00147-4 Smith N., Hartigan P ., 2006, ApJ, 638, 1045 Smith N., Gehrz R. D., Hinz P . M., Hoffmann W. F., Hora J. L., Mamajek E. E., Meyer M. R., 2003, AJ, 125, 1458 Smith N., Li W., Filippenko A. V ., Chornock R., 2011a, Monthly Notices of the Royal Astronomical Society, 412, 1522 Smith N., Li ...

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