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The Progenitor of the Type II-Plateau SN 2025pht in NGC 1637: The Dustiest, Most Luminous Red Supergiant So Far?

Schuyler D. Van Dyk, Tamas Szalai, Gagandeep S. Anand, Thomas G. Brink, Noah Zimmer, Dan Milisavljevic, Ori D. Fox, Jacob E. Jencson, WeiKang Zheng, Alexei V. Filippenko

Abstract

We provide a characterization of the red supergiant (RSG) progenitor candidate for the nearby Type II-plateau supernova (SN) 2025pht in NGC 1637. The star was first detectable in 2001 by the Hubble Space Telescope (HST) and then again in a dozen bands by the James Webb Space Telescope (JWST) in 2024. This "quasi-snapshot" of the star's nature almost immediately prior to explosion is unprecedented. The RSG varied in brightness, and we posit that it could have been a pulsating variable, possibly with a long period of ~660 days. The largest uncertainty is the host-galaxy distance, which we establish to be 10.73+/-1.76 Mpc. The star was also heavily extinguished by interstellar dust internal to the host, with visual extinction A_V(host)~1.7 mag (total A_V(tot)~1.8 mag). Dust radiative-transfer modeling reveals the star's circumstellar medium to be quite dusty and silicate-rich, yielding a bolometric luminosity log(L_bol/L_Sun)=5.08+/-0.16 and a cool effective temperature T_eff=2100--2500 K. The available HST optical data had no bearing on the shape of the candidate's observed spectral energy distribution -- for the first time, without the archival JWST observations we would not have been able to detect and characterize the candidate at all. The SN 2025pht progenitor candidate, although quite similar to that of SN 2023ixf, may be the most luminous candidate identified to date.

The Progenitor of the Type II-Plateau SN 2025pht in NGC 1637: The Dustiest, Most Luminous Red Supergiant So Far?

Abstract

We provide a characterization of the red supergiant (RSG) progenitor candidate for the nearby Type II-plateau supernova (SN) 2025pht in NGC 1637. The star was first detectable in 2001 by the Hubble Space Telescope (HST) and then again in a dozen bands by the James Webb Space Telescope (JWST) in 2024. This "quasi-snapshot" of the star's nature almost immediately prior to explosion is unprecedented. The RSG varied in brightness, and we posit that it could have been a pulsating variable, possibly with a long period of ~660 days. The largest uncertainty is the host-galaxy distance, which we establish to be 10.73+/-1.76 Mpc. The star was also heavily extinguished by interstellar dust internal to the host, with visual extinction A_V(host)~1.7 mag (total A_V(tot)~1.8 mag). Dust radiative-transfer modeling reveals the star's circumstellar medium to be quite dusty and silicate-rich, yielding a bolometric luminosity log(L_bol/L_Sun)=5.08+/-0.16 and a cool effective temperature T_eff=2100--2500 K. The available HST optical data had no bearing on the shape of the candidate's observed spectral energy distribution -- for the first time, without the archival JWST observations we would not have been able to detect and characterize the candidate at all. The SN 2025pht progenitor candidate, although quite similar to that of SN 2023ixf, may be the most luminous candidate identified to date.
Paper Structure (20 sections, 16 figures)

This paper contains 20 sections, 16 figures.

Table of Contents

  1. Introduction
  2. Observations
  3. Analysis
  4. Properties of the Supernova
  5. Photometry of the Progenitor Candidate
  6. Was The Progenitor Candidate Variable?
  7. Reddening To the Supernova
  8. Distance to the Host Galaxy
  9. The Inferred Properties of the Progenitor Candidate
  10. Discussion and Conclusions
  11. Estimations of Reddening to the SN
  12. Reddening From Interstellar Na i D
  13. Reddening from Spectral Comparison
  14. $B-V$ Color Comparison
  15. A Further Look at the $B-V$ Color Comparison
  16. ...and 5 more sections

Figures (16)

  • Figure 1: Portions of images in which the SN 2025pht site was serendipitously captured, all shown to the same orientation and scale. The site location corresponds to that of the progenitor candidate identified by Perez2025 and indicated by solid tickmarks in each panel. Panel (a) is a coaddition of all the HST WFPC2 F555W images obtained of the host galaxy from 2001 September 2 to October 31; panel (b) is a JWST NIRCam F405N image from 2024 October 8; panel (c) is a JWST MIRI F770W image from 2024 February 5; and, panel (d) is a MIRI image from the same date in F2100W. The candidate is well detected in both F405N and F770W, but not detected in either F555W or F2100W. North is up and east is to the left in all four panels. See also Kilpatrick2025.
  • Figure 2: Optical spectra of SN 2025pht from 2025 July 3 Strader2025, and from July 31, August 21, and August 30 (this study). Various spectral features, including telluric absorption, are indicated. Also shown for comparison are spectra at various ages of the SNe II-P SN 2007od and SN 2008M Gutierrez2017, SN 2013ej Dhungana2016, and SN 2023ixf Zheng2025. All spectra have been corrected for the redshifts of their host galaxies based on the values in NED. None of the spectra shown has been corrected for reddening.
  • Figure 3: Optical $BVI$ (Vega) light curves of SN 2025pht from Mikolajczyk2025. For comparison we show light curves in these bands for SN 2007od Inserra2011Anderson2024, SN 2008M Anderson2024, SN 2009bw Inserra2012, and SN 2013ej Valenti2014Bose2015Huang2015Dhungana2016Yuan2016; these curves have been shifted in brightness to provide a reasonable match with the SN 2025pht curves. No correction for reddening has been applied to any of the curves.
  • Figure 4: (a): Photometry from HST WFPC2 data from 2001 in F814W (see Table \ref{['tab:light_curve']}). Also shown are simple sinusoid models with periods of 470 and 660 days. (b) Photometry from HST WFC3/UVIS F814W and JWST NIRCam F150W, F187N, and F335M data from 2024 (see Table \ref{['tab:observations']}). Also displayed are the same sinusoid models shown in panel (a), which best fit the 2001 data, do not violate the 2024 F814W upper limit, and are in reasonable agreement with the NIRCam data.
  • Figure 5: A compendium of all of the known distance estimates to the host galaxy NGC 1637. The estimates we have culled from the literature are shown as filled circles. Also included here are estimates we have made in this study, based on SCM measurements to SN 1999em (filled squares) and SN 2025pht (filled triangle), as well as a JAGB-based measurement from the archival JWST observations of the host (filled diamond). In addition, we show the weighted mean of all the distances we have considered here (filled star).
  • ...and 11 more figures