An international team of astronomers has performed follow-up observations of a peculiar Type Ia supernova designated SN 2023vjh. Results of the observational campaign, published July 9 on the preprint server arXiv, deliver important insights into the nature of this explosion.
Stellar explosions and their peculiar subluminous subclass
Supernovae (SNe) are powerful, luminous stellar explosions. They are important to the scientific community because they offer essential clues about the evolution of stars and galaxies. In general, SNe are divided into two groups based on their atomic spectra: Type I (no hydrogen in their spectra) and Type II (showcasing hydrogen spectral lines).
Type Ia supernovae (SN Ia) are found in binary systems in which one of the stars is a white dwarf. Stellar explosions of this type also offer essential clues about the evolution of stars and galaxies.
However, apart from normal SNe Ia, some subtypes present characteristics that differ from those of normal supernovae of this type, suggesting various explosion mechanisms. One is the subluminous subclass of 91bg-like SNe (named after the prototype SN 1991bg), which exhibits strong silicon absorption and absorption features from several intermediate-mass elements. Moreover, they are characterized by relatively low ejecta velocities.
All eyes on distant explosion
SN 2023vjh is a 91bg-like SN Ia discovered Oct. 17, 2023, by the Zwicky Transient Facility (ZTF) with a magnitude of 21.18 in the g-ZTF band. The supernova is possibly associated with MCG+04-10-013—an elliptical galaxy at a distance of some 271 million light-years from Earth. The explosion took place approximately 22,000 light-years from the center of this galaxy.
Shortly after its discovery, a follow-up photometric and spectroscopic campaign of SN 2023vjh was initiated, employing various ground-based telescopes worldwide. Now, astronomers led by Maria Kopsacheili of the Institute of Space Sciences in Barcelona, Spain, have announced results from these observations.
According to the new findings, SN 2023vjh had a rise time of 11.6 days. The optical spectra of the supernova, spanning −8.6 to +47.3 days relative to its maximum brightness in the B band, show the typical 91bg-like features, pointing to a cool photosphere. The reddening of SN 2023vjh was found to be relatively large—at a level of 0.2–0.35 mag.
Furthermore, measured expansion velocities and pseudo-equivalent widths confirm that SN 2023vjh is an extremely cool event. In addition, late-phase near-infrared spectra of the supernova at three epochs reveal absorption features of calcium, iron and cobalt, complementing the optical data, as well as the absence of the H-band break feature, which represents a sharp drop in flux caused by the onset of iron-peak elements.
An unusual 91bg-like event
The researchers concluded that, overall, the photometric and spectral properties of SN 2023vjh are generally consistent with those of other well-studied 91bg-like events. However, the investigated supernova appears to be a special case within this subclass, as its dimness and inferred reddening are unusually high compared with typical 91bg-like SNe.
“These results show that SN 2023vjh is an unusually faint, fast-declining 91bg-like supernova. Its systematically fainter light curves, despite the lack of clear host-galaxy extinction signatures, make it a distinctive case within this subclass. A contribution from circumstellar material affecting the observed reddening cannot be excluded and may represent an interesting possibility for this event,” the authors of the paper concluded.
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Publication details
M. Kopsacheili et al, The type Ia supernova 2023vjh: a peculiar 1991bg-like SN with unusually faint light curves, arXiv (2026). DOI: 10.48550/arxiv.2607.08821
Journal information:
arXiv
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Observations investigate the nature of a peculiar supernova (2026, July 19)
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