The Chinese Academy of Sciences (CAS) recently conducted a comprehensive study of a peculiar Type IIP supernova, designated as SN 2024abfl, using the 2.4-meter Lijiang and 2.16-meter Xinglong telescopes. This observational campaign utilized both optical photometric and spectroscopic techniques to decode the physical properties of this stellar explosion located within the galaxy NGC 2146. The resulting data provides critical evidence regarding the progenitor’s nature, highlighting a core-collapse event characterized by unusually low luminosity and expansion velocities.
SN 2024abfl: morphological classification and stellar progenitor models
Astronomers typically categorize Type II supernovae into two distinct classes based on the specific shape of their light curves following the peak of luminosity. Type II-Linear (SNe IIL) supernovae are identified by a relatively rapid and linear decline in brightness, whereas Type II-Plateau (SNe IIP) events maintain a consistent level of brilliance for an extended period. In a standard SN IIP, this “plateau” phase, driven by hydrogen recombination, generally persists for approximately 100 days before transitioning to the radioactive decay tail.
These plateau-type events are theoretically linked to progenitor stars that manage to retain a significant portion of their hydrogen-rich envelopes, often estimated at more than three solar masses, prior to the final collapse. Despite extensive research over the past two decades, many fundamental properties of these supernovae remain subject to scientific debate. The study of outliers like SN 2024abfl is essential for refining these models, as they represent the lower energy limits of what a massive star can produce during its terminal phase.
SN 2024abfl stands out as a low-luminosity specimen within the Type IIP family, exhibiting a redshift of approximately 0.003 within its host environment. Its unique profile is defined by an exceptionally long-lasting plateau and expansion speeds that are remarkably slower than those seen in typical core-collapse events. These characteristics prompted the CAS research team to investigate the specific mass and energy constraints that could lead to such a faint yet enduring stellar explosion.
Distance constraints and intrinsic physical parameters
A primary challenge faced by the research team led by Luhan Li involved establishing an accurate distance for the host galaxy NGC 2146. This measurement is vital because it directly constrains the progenitor’s initial mass, the absolute magnitude of the event, and the total kinetic energy released during the explosion. Without a precise distance value, it is impossible to determine whether the supernova’s perceived faintness is an intrinsic property or merely a result of its spatial positioning.
Previous academic literature provided a wide range of distance estimates for NGC 2146, varying from 31 to over 54 million light-years, primarily due to the galaxy’s irregular and distorted morphology. This irregularity is likely the result of tidal interactions with a nearby low-surface-brightness companion, which complicates standard astronomical distance markers. The current study refined these estimates to a range between 28.5 and 32.4 million light-years, allowing for a more stable calculation of the supernova’s energy output.
The analysis confirmed that SN 2024abfl is an intrinsically weak explosion, with a plateau luminosity measured at roughly 100 duodecillion ergs per second. Even when applying the most conservative (higher) distance estimates, the event remains one of the faintest Type IIP supernovae ever recorded. Furthermore, the light curve demonstrated a plateau duration of 110 days, suggesting a substantial hydrogen envelope that required an extended period to fully recombine and cool.
Spectroscopic dynamics and the core-collapse hypothesis
The spectroscopic data revealed that SN 2024abfl synthesized an incredibly small amount of radioactive nickel-56, estimated between 0.002 and 0.004 solar masses. This low nickel yield is a classic signature of a low-energy explosion, indicating that the progenitor star was likely at the lowest mass threshold capable of undergoing a core collapse. The lack of radioactive heating explains why the supernova’s brightness dropped so significantly once the hydrogen recombination phase concluded.
Furthermore, the expansion velocities observed in the spectral lines were exceptionally low, with iron (Fe II) velocities measured at just 1,200 km/s approximately 50 days after the explosion. This is a stark contrast to standard Type IIP supernovae, where such velocities are typically much higher. These slow-moving ejecta provide further evidence for a “weak” explosion mechanism, where the energy released was barely sufficient to overcome the gravitational binding energy of the progenitor star.
Based on these integrated findings, the researchers conclude that SN 2024abfl originated from a very low-mass core-collapse event. The observed color evolution, plateau duration, and the specific magnitude drop-off are more consistent with this scenario than with alternative electron-capture supernova models. While this interpretation is robust, the authors emphasize that obtaining even more precise distance measurements will be necessary to finalize the explosion parameters and fully understand this rare class of stellar deaths.
The study is published on arXiv.
