SN 2024abfl: A Low-Luminosity Type IIP Supernova in NGC 2146 from a Low-Mass Red Supergiant Progenitor

Type IIP supernovae (SNe IIP) exhibit a significant diversity in their explosion properties, yet the physical mechanisms driving this diversity remain unknown. In this work, we present photometric and spectroscopic observations of SN 2024abfl, a SN IIP in NGC 2146 with a directly detected red supergiant (RSG) progenitor. We find it has a low plateau luminosity ($M_V \sim -15$ mag) and a relatively long plateau length ($\sim 126.5$ days). By fitting a semi-analytical model, we estimated a $^{56}$Ni mass of $\sim 0.009 M_\odot$, an initial kinetic energy of $\sim 0.42$ foe, an initial thermal energy of $\sim 0.03$ foe and an ejecta mass of $\sim 8.3 M_\odot$. The spectral evolution of SN 2024abfl is similar to those of other SNe IIP, except for much lower ejecta velocities at similar epochs. At later epochs, we find a relatively high-velocity H$α$ absorption feature at $\sim -4000$ km s$^{-1}$, possibly due to a fast-moving plume of matter in the inner ejecta, and two emission features at $\pm 2000$ km s$^{-1}$, possibly caused by CSM interaction. We estimate the progenitor mass to be $\le 15 M_\odot$ based on nebular spectra. We conclude that SN 2024abfl is a low-luminosity SN IIP originating from a low-mass RSG progenitor.

💡 Research Summary

This paper presents a comprehensive observational study of SN 2024abfl, a Type IIP supernova discovered on 2024 November 15 in the starburst galaxy NGC 2146. The supernova was identified at an apparent magnitude of 17.5 mag in a clear band and is located in the outskirts of its host, a region with relatively low background contamination. Crucially, pre‑explosion Hubble Space Telescope images reveal a red supergiant (RSG) at the SN position, allowing a direct progenitor identification. Photometric monitoring was carried out with a network of facilities—including the Xinglong 60‑cm and 35‑cm telescopes, the Thai Robotic Telescope network, the Liverpool Telescope, ZTF, ATLAS, and Swift/UVOT—covering the ultraviolet (UVW2, UVM2, UVW1) and optical (g, r, i, B, V, R, I) bands from 4.4 days up to 379 days after explosion. Standard image reduction (bias subtraction, flat‑fielding) and PSF photometry were performed; because the SN lies far from the host nucleus, host subtraction was unnecessary. The resulting light curves show a plateau phase lasting 126.5 days with an absolute V‑band magnitude of ≈ –15 mag, placing SN 2024abfl firmly in the low‑luminosity Type IIP (LL‑IIP) subclass.

Spectroscopic observations were obtained with the Xinglong 2.16‑m telescope, the Nordic Optical Telescope (2.56 m), Gemini‑North (GMOS), and the Himalayan Chandra Telescope (HFOSC) from 2.6 days to 198.6 days post‑explosion. The early spectra (≈ 5 days) display the classic P‑Cygni profiles of H α, H β, Fe II, and Sc II, but the absorption minima correspond to velocities of only ~3000 km s⁻¹, significantly lower than typical IIP values (~5000 km s⁻¹). This low expansion velocity is consistent with the modest kinetic energy inferred from light‑curve modeling. At later epochs (~150 days) a high‑velocity H α absorption component at –4000 km s⁻¹ appears, together with two symmetric emission features at ±2000 km s⁻¹. The authors interpret these as signatures of a fast‑moving plume in the inner ejecta and possible circum‑stellar material (CSM) interaction, respectively. Nebular‑phase spectra (> 200 days) show relatively weak