The nebular phase of SN 2024ggi: a low-mass progenitor with no signs of interaction

TL;DR

This study uses nebular-phase optical spectroscopy (days 287–400) and multi-band photometry to characterize SN 2024ggi, a nearby Type II supernova. By analyzing emission-line profiles and line ratios, and constructing a bolometric light curve from optical to IR data, the authors constrain the progenitor to a ZAMS mass of $12-15\,M_\odot$ and derive a nickel mass of $M_{\mathrm{Ni}} \approx 0.05-0.06\,M_\odot$, with strong evidence for near-complete $\gamma$-ray trapping and no circumstellar interaction up to 400 days. The line profiles imply a largely symmetric ejecta, with a possible oxygen-rich clump moving toward the observer, and the results are broadly consistent with similar low-mass progenitor inferences from nebular modeling. Together, these findings reinforce the view that SN 2024ggi originated from a relatively low-mass red supergiant and highlight the diagnostic power of nebular-phase observations for constraining progenitor properties in core-collapse SNe.

Abstract

Context: SN 2024ggi is a Type II supernova (SN) discovered in the nearby galaxy NGC 3621 (D $\approx6.7\pm0.d$ Mpc) on 2024 April 03.21 UT. Its proximity enabled a detailed investigation of the SN's properties and its progenitor star. This work focuses on the optical evolution of SN 2024ggi at the nebular phase. Aims: We investigate the progenitor properties and possible asymmetries in the ejecta by studying the nebular phase evolution between days 287 and 400 after the explosion. Methods: We present optical photometry and spectroscopy of SN 2024ggi during the nebular phase, obtained with the Las Campanas and Gemini South Observatories. Four nebular spectra were taken at 287, 288, 360, and 396 days post-explosion, supplemented by late-time $uBVgri$-band photometry spanning $320-400$ days. The analysis of the nebular emission features is performed to probe ejecta asymmetries. Based on the [O I] flux and [O I]/[Ca II] ratio, and comparisons with spectra models from the literature, we arrive to an estimate of the progenitor mass. Additionally, we construct the bolometric light curve from optical photometry and near-infrared data to derive the synthesized nickel mass. Results: Our analysis suggests a progenitor zero-age-main-sequence mass between $12-15 M_\odot$. The late-time bolometric light curve is consistent with a synthesized $^{56}$Ni mass of $0.05-0.06 M_\odot$. The line profiles exhibit only minor changes over the observed period and suggest a roughly symmetrical ejecta, with a possible clump of oxygen-rich material moving towards the observer. No signatures of circumstellar material interaction are detected up to 400 days after the explosion.

Figures (7)

• Figure 1:
• Figure 2: Nebular spectra of SN 2024ggi compared with SN 2023ixf, SN 2004et and SN 199em. All spectra have been corrected by their reported redshift and scaled by the mean value in the region between $7600-8400$ Å. Emission lines are marked in gray dotted lines.
• Figure 3: Gaussian decomposition of the [Oi]$\lambda\lambda6300,6364$ and H$\alpha$ line profiles in the spectrum of SN 2024ggi at 287 days. Panel a): three-Gaussian fitting of the [Oi] doublet, with a wide component centered nearly at the rest wavelength (i.e., 6300 Å). Panel b): four-Gaussian fitting of the [Oi] doublet with the separation of the two wide emissions fixed at 64 Å. Panel c): three-Gaussian fitting of the H$\alpha$ line, resulting in a wide component centered at rest. In Table \ref{['tab:fitting']}, all FWHM and peak velocities are detailed for the three fittings.
• Figure 4: Optical light curves of SN 2024ggi. The new data published in this work correspond to the Gemini and Swope telescopes. Early phase data is published by Ertini2025. The black vertical lines indicate the phases of the four spectra presented in this work. The dotted gray line indicates the epoch where the $o$-, $r$-, and $i$-band light curves show a slope break, also noticeable in the ATLAS o-band light curve (see Sect. \ref{['sec:LC']}). Inset shows an expanded view of the temporal evolution between $320-415$ days, highlighting the change in decline rate. Solid lines represent separate linear fits to the data before and after 365 days (marked by the vertical dotted line).
• Figure 5: Bolometric light curve of SN 2024ggi. The bolometric light curve published in Ertini2025 and their preferred model are plotted in pink dots and line, respectively. Our fitting of Eq. \ref{['eq:Ni_mass']} is shown in purple. A new hydrodynamical model with the same parameters as those presented in Ertini2025, but with a larger $^{56}$Ni mass of $0.052~M_\odot$ is shown in the cyan line. The dashed gray line indicates the decay with a $^{56}$Ni mass of $0.049~M_\odot$ and full-trapping of $\gamma$ rays.