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SN 2024cld: unveiling the complex mass-loss histories of evolved supergiant progenitors to core collapse supernovae

T. L. Killestein, M. Pursiainen, R. Kotak, P. Charalampopoulos, J. Lyman, K. Ackley, S. Belkin, D. L. Coppejans, B. Davies, M. J. Dyer, L. Galbany, B. Godson, D. Jarvis, N. Koivisto, A. Kumar, M. Magee, M. Mitchell, D. O'Neill, A. Sahu, B. Warwick, R. P. Breton, T. Butterley, Y. -Z. Cai, J. Casares, V. S. Dhillon, N. Elias-Rosa, M. Fraser, D. K. Galloway, B. Gompertz, M. González-Bañuelos, C. P. Gutiérrez, T. Kangas, E. Kankare, L. Kelsey, T. Kravtsov, G. Leloudas, S. P. Littlefair, K. Matilainen, S. Mattila, T. Nagao, K. Noysena, L. K. Nuttall, P. O'Brien, D. Pollacco, G. Ramsay, A. Reguitti, T. M. Reynolds, I. Salmaso, R. L. C. Starling, D. Steeghs, M. Stritzinger, K. Ulaczyk, G. Valerin, Z. -Y. Wang, R. Wilson

Abstract

Pre-explosion mass loss in supernova (SN) progenitors is a crucial unknown factor in stellar evolution, yet has been illuminated recently by the diverse zoo of interacting transients. We present SN2024cld, a transitional core-collapse SN at a distance of 39 Mpc, straddling the boundary between SN II and SN IIn, showing persistent interaction with circumstellar material (CSM) similar to H-rich SN1998S and PTF11iqb. The SN was discovered and classified just 12h post-explosion via the GOTO-FAST high-cadence program. Optical spectroscopy, photometry, and polarimetry over 220d chart the complex, long-lived interaction in this transient. Early evolution is dominated by CSM interaction, showing a 14d rise to a peak absolute magnitude of g=-17.6 mag, with clear flash-ionisation signatures. SN2024cld also shows a slowly-evolving late time light curve powered by CSM interaction, with high-velocity (6000 km/s) shoulders on a strong multi-component H-alpha profile. Dense polarimetric coverage reveals marked evolution in the photospheric geometry -- peaking at p=2% 10 days post-explosion, and rotating approx. 60 deg as the ejecta sweep more distant CSM. We observe a narrow 60 km/s H-alpha P Cygni feature throughout, associated with pre-shock CSM. SN2024cld represents among the best-observed 98S-like SNe to date, revealing a multi-component CSM structure: a dense, inner aspherical envelope, CSM disk/torus, and tenuous, extended wind. We propose this SN arose from an evolved supergiant progenitor experiencing multiple mass loss episodes in its terminal years, with binary interaction plausibly generating the CSM disk. SN2024cld constrains the progenitors and mass-loss paradigms of 98S-like SNe, unveiling the chaotic ends of evolved supergiant stars from afar.

SN 2024cld: unveiling the complex mass-loss histories of evolved supergiant progenitors to core collapse supernovae

Abstract

Pre-explosion mass loss in supernova (SN) progenitors is a crucial unknown factor in stellar evolution, yet has been illuminated recently by the diverse zoo of interacting transients. We present SN2024cld, a transitional core-collapse SN at a distance of 39 Mpc, straddling the boundary between SN II and SN IIn, showing persistent interaction with circumstellar material (CSM) similar to H-rich SN1998S and PTF11iqb. The SN was discovered and classified just 12h post-explosion via the GOTO-FAST high-cadence program. Optical spectroscopy, photometry, and polarimetry over 220d chart the complex, long-lived interaction in this transient. Early evolution is dominated by CSM interaction, showing a 14d rise to a peak absolute magnitude of g=-17.6 mag, with clear flash-ionisation signatures. SN2024cld also shows a slowly-evolving late time light curve powered by CSM interaction, with high-velocity (6000 km/s) shoulders on a strong multi-component H-alpha profile. Dense polarimetric coverage reveals marked evolution in the photospheric geometry -- peaking at p=2% 10 days post-explosion, and rotating approx. 60 deg as the ejecta sweep more distant CSM. We observe a narrow 60 km/s H-alpha P Cygni feature throughout, associated with pre-shock CSM. SN2024cld represents among the best-observed 98S-like SNe to date, revealing a multi-component CSM structure: a dense, inner aspherical envelope, CSM disk/torus, and tenuous, extended wind. We propose this SN arose from an evolved supergiant progenitor experiencing multiple mass loss episodes in its terminal years, with binary interaction plausibly generating the CSM disk. SN2024cld constrains the progenitors and mass-loss paradigms of 98S-like SNe, unveiling the chaotic ends of evolved supergiant stars from afar.

Paper Structure

This paper contains 24 sections, 3 equations, 20 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Observations and data reduction
  3. Survey photometry
  4. Optical photometry
  5. Infrared photometry
  6. UV photometry and X-ray upper limits
  7. Optical spectroscopy
  8. Imaging polarimetry
  9. Host galaxy and environment
  10. Photometry
  11. Explosion time and peak
  12. Bolometric light curve
  13. Constraints on pre-explosion outbursts
  14. Spectroscopy
  15. Early time: flash-ionised phase
  16. ...and 9 more sections

Figures (20)

  • Figure 1: NOT/ALFOSC $gri$ deep stack showing SN 2024cld (circled), embedded in the spiral arm of host galaxy NGC 6004. The panels above show the GOTO discovery/template/difference image for SN 2024cld.
  • Figure 2: The top panels correspond to reconstructed $r$-band and H$\alpha$ images of NGC 6004, the host galaxy of SN 2024cld, generated from the CALIFA/PMAS merged data cubes. The dark blue circle shows the 1 radius aperture centred on the explosion site of SN 2024cld used to derive the explosion site spectrum. An H II region is visible just off the edge of the explosion site, likely yielding some of the narrow line components seen in later-time spectra. The explosion site spectrum is plotted in the bottom panel, with relevant host lines used to fit for the redshift overplotted.
  • Figure 3: Host-subtracted photometry of SN 2024cld, corrected for Galactic and host reddening. The light curve shows three key stages: a rapid rise to peak in $\sim$ 10 days, a plateau phase between 50-100 days post-explosion, and then a second plateau beginning around 110 days post-explosion. Non-detections are plotted as downwards-facing triangles. The explosion date is estimated from joint fitting of survey photometry (see Section \ref{['sec:explosion-fit']}). Vertical tick-marks indicate the epochs on which spectroscopy was obtained. Error bars correspond to the $1\sigma$ photometric uncertainties. The two shaded regions mark the first and second plateaus referred to in the text.
  • Figure 4: Pre-peak detections and upper limits for SN 2024cld, overplotted with the model light curve for each survey used to infer the explosion date, which is marked with the dashed vertical line. Shaded regions correspond to the 1$\sigma$ confidence interval, estimated from posterior draws from the model. The triangles represent 5$\sigma$ non-detections. Offsets (given in the legend) are applied to the ATLAS photometry to enhance visibility. The inset histogram shows samples of the $t_\mathrm{expl}$ parameter to emphasise the tight constraints possible with generative modelling, plotted as UTC time on 2024 February 12.
  • Figure 5: Top: pseudo-bolometric light curve of SN 2024cld. Middle: Evolution of the blackbody (BB) radius of SN 2024cld. Bottom: Temperature evolution of SN 2024cld. The vertical lines across all panels show the end of the flash-ionised phase (FI), (approximate) start of plateau 1 (P1), and (approximate) start of plateau 2 (P2) to guide the eye. In all panels, the error bars correspond to the 1$\sigma$ uncertainty.
  • ...and 15 more figures