Early panchromatic spectra reveal helium in the thermonuclear supernova 2024kce
Abstract
Faint Type I supernovae blur the boundaries between spectroscopic classes, obscuring their progenitors and explosion mechanisms. One proposed origin is a double detonation, in which ignition of an accreted helium shell triggers the explosion of a carbon oxygen white dwarf. Surviving helium is a direct prediction of this mechanism, but its strongest near-infrared feature overlaps with carbon and is ambiguous in isolation. Here we present SN 2024kce, observed with simultaneous optical and near-infrared spectroscopy eleven days before maximum light. We identify He I absorption at three wavelengths, all consistent with a velocity of 16,400 km/s, well above the photosphere. This is the first detection of helium before maximum light in a thermonuclear supernova. Helium at these velocities requires nearby radioactive material for non-thermal excitation, pointing to ash from a detonated surface helium shell. A double detonation model reproduces the optical spectral evolution, suppressed blue flux, and He I 1.083 micron absorption feature. SN 2024kce shares properties with both subluminous Type Ia supernovae and Ia-like calcium-rich transients, providing evidence that the same explosion mechanism operates across these classes. From early optical and near-infrared spectra to Rubin's First Look images, SN 2024kce showcases the full reach of modern observatories in exposing the physics of rare explosions.
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BibTeX
@misc{polin2026early,
title = {{Early panchromatic spectra reveal helium in the thermonuclear supernova 2024kce}},
author = {Abigail Polin and Dillon Hasenour and Sahana Kumar and Willem Hoogendam and Jing Lu and Daniel Polin and Danielle Dickinson and Braden Garretson and Nidia Morrell and Huei Sears and Katie Auchettl and Teresa Boland and Christopher Burns and Kenneth C. Chambers and Dhvanil Desai and Jason T. Hinkle and Thressay Hoover and Eric Hsiao and Mark E. Huber and David O. Jones and Colin Macrie and Bailey Martin and Cameron Pfeffer and Miranda Pikus and Benjamin J. Shappee and Madeline Taylor and Brad E. Tucker and Michael Tucker and Huangfei Xiao},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.30674},
eprint = {2610.30674},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.30674},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Early panchromatic spectra reveal helium in the thermonuclear supernova 2024kce
AU - Abigail Polin
AU - Dillon Hasenour
AU - Sahana Kumar
AU - Willem Hoogendam
AU - Jing Lu
AU - Daniel Polin
AU - Danielle Dickinson
AU - Braden Garretson
AU - Nidia Morrell
AU - Huei Sears
AU - Katie Auchettl
AU - Teresa Boland
AU - Christopher Burns
AU - Kenneth C. Chambers
AU - Dhvanil Desai
AU - Jason T. Hinkle
AU - Thressay Hoover
AU - Eric Hsiao
AU - Mark E. Huber
AU - David O. Jones
AU - Colin Macrie
AU - Bailey Martin
AU - Cameron Pfeffer
AU - Miranda Pikus
AU - Benjamin J. Shappee
AU - Madeline Taylor
AU - Brad E. Tucker
AU - Michael Tucker
AU - Huangfei Xiao
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.30674
UR - https://arxiv.org/abs/2610.30674
AB - Faint Type I supernovae blur the boundaries between spectroscopic classes, obscuring their progenitors and explosion mechanisms. One proposed origin is a double detonation, in which ignition of an accreted helium shell triggers the explosion of a carbon oxygen white dwarf. Surviving helium is a direct prediction of this mechanism, but its strongest near-infrared feature overlaps with carbon and is ambiguous in isolation. Here we present SN 2024kce, observed with simultaneous optical and near-infrared spectroscopy eleven days before maximum light. We identify He I absorption at three wavelengths, all consistent with a velocity of 16,400 km/s, well above the photosphere. This is the first detection of helium before maximum light in a thermonuclear supernova. Helium at these velocities requires nearby radioactive material for non-thermal excitation, pointing to ash from a detonated surface helium shell. A double detonation model reproduces the optical spectral evolution, suppressed blue flux, and He I 1.083 micron absorption feature. SN 2024kce shares properties with both subluminous Type Ia supernovae and Ia-like calcium-rich transients, providing evidence that the same explosion mechanism operates across these classes. From early optical and near-infrared spectra to Rubin's First Look images, SN 2024kce showcases the full reach of modern observatories in exposing the physics of rare explosions.
ER -