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arXiv · 2606.30796

NLTE Spectral Modelling of the Nearby Stripped-Envelope Supernova 2024ehs

Wilmer Sand Hellman·Seán J. Brennan·Stan Bartmentloo·Christoffer Fremling·Anjasha Gangopadhyay·Anders Jerkstrand·Ragnhild Lunnan·Josiah Purdum·Steve Schulze·Jesper Sollerman
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Abstract

We present a detailed study of the Type IIb supernova 2024ehs, discovered in March 2024 in the nearby galaxy NGC 3443 at a distance of $23.8\pm 0.9$ Mpc. Using photometric and spectroscopic observations spanning 10 months, we analyse its light curve, spectral evolution, and physical properties with the \texttt{SUMO} radiative transfer code. SN 2024ehs exhibits a narrow light-curve peak, rapid decline, and weak helium lines, distinguishing it from typical Type IIb supernovae. Comparisons with other objects, including SNe 1993J and 2020acat, and modelling of nebular spectra suggest a low ejecta mass, high velocities ($\sim$20,000 \kms), and a $^{56}$Ni mass just below $\sim0.1 \, \mathrm{M}_{\odot}$. Furthermore, the nebular spectral models indicate a progenitor with a helium core mass of $\sim 6 \, \mathrm{M}_{\odot}$, consistent with a zero-age main-sequence mass of $\sim 23\, \mathrm{M}_{\odot}$. The composition of spectra is explored through photospheric modelling, finding a link between expansion velocity and the relative strength of different element lines. This work discusses further the diversity of stripped-envelope supernovae and the role of binary interactions for their progenitors, and demonstrates the need for further modelling to refine $^{56}$Ni mass estimates and to understand the physical mechanisms driving their evolution.

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Wilmer Sand Hellman, Seán J. Brennan, Stan Bartmentloo, Christoffer Fremling, Anjasha Gangopadhyay, Anders Jerkstrand, Ragnhild Lunnan, Josiah Purdum, Steve Schulze, Jesper Sollerman. 2026-06-29. NLTE Spectral Modelling of the Nearby Stripped-Envelope Supernova 2024ehs. https://arxiv.org/abs/2606.30796

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