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SN 2024abfl: A Flat-Plateau, Low-Luminosity Type IIP Supernova with Early CSM Interaction

Madison Gerard, Jennifer E. Andrews, Geoffrey C. Clayton, David J. Sand, K. Azalee Bostroem, Jeniveve Pearson, Raya Dastidar, Aravind P. Ravi, Conor L. Ransome, Bhagya Subrayan, Griffin Hosseinzadeh, Brian Hsu, Yize Dong, Manisha Shrestha, Stefano Valenti, Nathan Smith, Daryl Janzen, M. J. Lundquist, Nicolas Meza, Saurabh W. Jha, Kate D. Alexander, Collin Christy, Noah Franz, Lindsey A. Kwok, Moira Andrews, Joseph Farah, Daichi Hiramatsu, D. Andrew Howell, Curtis McCully, Kathryn Wynn, Reka Konyves-Toth, Xiaofeng Wang

TL;DR

SN 2024abfl is a nearby, low-luminosity Type IIP SN that exhibits an unusually flat ~125-day plateau and signs of early ejecta–CSM interaction. The study combines high-cadence photometry, multi-epoch spectroscopy (including an early broad 4600 Å ledge), and both analytic shock-cooling and 1D hydrodynamical modeling to infer a weak explosion from a ~9–12 solar mass red supergiant, with a small $M(^{56}$Ni) ≈ 0.01 M⊙. Nebular-phase spectra support Fe-core-collapse in a low-mass progenitor, while early-time CSM signatures indicate pre-explosion mass loss and complex ejecta-CSM geometry (including possible disc-like CSM). Together, these findings place SN 2024abfl among LL SNe II that reveal a continuum between ECSN and iron-core-collapse outcomes and underscore the importance of rapid, comprehensive follow-up for constraining pre-supernova mass loss in massive stars.

Abstract

We present photometric and spectroscopic observations of SN 2024abfl, a low-luminosity Type IIP supernova (LLSN) discovered shortly after explosion. The transient reached a peak absolute magnitude of $M_V = -14.9$ and exhibited an extended, flat plateau lasting $\sim$125 days. From the late-time bolometric light curve, we estimate a $^{56}$Ni mass of $\sim0.01~M_\odot$, consistent with other LLSNe. Analytical shock-cooling models fail to reproduce the rapid early rise, indicating that circumstellar material (CSM) interaction contributed to the initial emission. The spectroscopic evolution is typical of LLSNe, with relatively narrow metal lines and low expansion velocities ($\lesssim 3000$ km s$^{-1}$) that decline slowly over time. We detect a broad ``ledge'' feature around 4600 Åwithin three days of explosion, which we interpret as a blend of high-ionization shock-accelerated CSM lines. Multi-peaked H$α$ profiles develop during the plateau phase, consistent with complex ejecta-CSM interactions. As one of the best-observed examples of LLSNe, SN 2024abfl exhibits a weak explosion and signatures of nearby CSM, offering new insights into progenitor properties, pre-explosion mass loss, and the diversity of LLSNe.

SN 2024abfl: A Flat-Plateau, Low-Luminosity Type IIP Supernova with Early CSM Interaction

TL;DR

SN 2024abfl is a nearby, low-luminosity Type IIP SN that exhibits an unusually flat ~125-day plateau and signs of early ejecta–CSM interaction. The study combines high-cadence photometry, multi-epoch spectroscopy (including an early broad 4600 Å ledge), and both analytic shock-cooling and 1D hydrodynamical modeling to infer a weak explosion from a ~9–12 solar mass red supergiant, with a small Ni) ≈ 0.01 M⊙. Nebular-phase spectra support Fe-core-collapse in a low-mass progenitor, while early-time CSM signatures indicate pre-explosion mass loss and complex ejecta-CSM geometry (including possible disc-like CSM). Together, these findings place SN 2024abfl among LL SNe II that reveal a continuum between ECSN and iron-core-collapse outcomes and underscore the importance of rapid, comprehensive follow-up for constraining pre-supernova mass loss in massive stars.

Abstract

We present photometric and spectroscopic observations of SN 2024abfl, a low-luminosity Type IIP supernova (LLSN) discovered shortly after explosion. The transient reached a peak absolute magnitude of and exhibited an extended, flat plateau lasting 125 days. From the late-time bolometric light curve, we estimate a Ni mass of , consistent with other LLSNe. Analytical shock-cooling models fail to reproduce the rapid early rise, indicating that circumstellar material (CSM) interaction contributed to the initial emission. The spectroscopic evolution is typical of LLSNe, with relatively narrow metal lines and low expansion velocities ( km s) that decline slowly over time. We detect a broad ``ledge'' feature around 4600 Åwithin three days of explosion, which we interpret as a blend of high-ionization shock-accelerated CSM lines. Multi-peaked H profiles develop during the plateau phase, consistent with complex ejecta-CSM interactions. As one of the best-observed examples of LLSNe, SN 2024abfl exhibits a weak explosion and signatures of nearby CSM, offering new insights into progenitor properties, pre-explosion mass loss, and the diversity of LLSNe.
Paper Structure (22 sections, 17 figures)

This paper contains 22 sections, 17 figures.

Table of Contents

  1. Introduction
  2. Discovery, Distance, and Reddening
  3. Discovery and Classification
  4. Archival HST data
  5. Distance and Reddening
  6. Observations and Data Reduction
  7. Photometry
  8. Spectroscopy
  9. Photometric Evolution
  10. Optical and UV Lightcurves
  11. Color Evolution
  12. Bolometric Lightcurve and $^{56}$Ni Mass
  13. Early Lightcurve Modeling
  14. 1D Hydrodynamical Modeling
  15. Spectroscopic Evolution
  16. ...and 7 more sections

Figures (17)

  • Figure 1: Composite $g,r,i$ image of SN 2024abfl in NGC 2146 obtained by Las Cumbres Observatory on 2024 December 4. The SN location is marked with white crosshairs.
  • Figure 2: Optical photometry of SN 2024abfl with offsets and telescope indicated in the legend. The adopted explosion epoch is MJD 60627.91. The right panel expands the first week.
  • Figure 3: Absolute V-band light curve of SN 2024abfl compared with other Type II SNe: 2003Z 2014MNRAS.439.2873S, 2005cs 2009MNRAS.394.2266P, 2012A 2013MNRAS.434.1636T, 2017eaw 2019ApJ...876...19S, 2018is 2025AA...694A.260D, 2018lab 2023ApJ...945..107P, 2018zd 2020MNRAS.498...84Z2022AstBu..77..407T, and 2023axu 2024ApJ...961..247S. SN 2024abfl has a peak V-band magnitude of $-14.87$ mag.
  • Figure 4: SN 2024abfl shown in the context of the SN II population from 2016MNRAS.459.3939V, plotted as peak absolute V-band magnitude versus plateau decline rate ($S_{50V}$; top) and plateau duration ($t_{\mathrm{PT}}$; bottom). Several well-studied LLSNe are highlighted in blue for reference.”
  • Figure 5: Extinction corrected $B-V$ color for SN 2024abfl compared with other SNe II, including other LLSNe. The adopted $E(B-V)_\mathrm{tot} =0.28$ mag is consistent with the color evolution of these similar SNe.
  • ...and 12 more figures