SN 2023xgo: Helium-rich Type Icn or Carbon-Flash Type Ibn supernova?

Gangopadhyay, A ORCID: 0000-0002-3884-5637, Sollerman, J ORCID: 0000-0003-1546-6615, Tsalapatas, K, Maeda, K ORCID: 0000-0003-2611-7269, Dukiya, N, Schulze, S, Fransson, C, Sarin, N ORCID: 0000-0003-2700-1030, Pessi, PJ ORCID: 0000-0002-8041-8559, Singh, M, Wise, J ORCID: 0000-0003-0733-2916, Nakaoka, T, Singh, A, Dastidar, R ORCID: 0000-0001-6191-7160, Kawabata, M, Qin, Y-J, Das, KK, Perley, D ORCID: 0000-0001-8472-1996, Fremling, C, Taguchi, K ORCID: 0000-0002-8482-8993 et al SN 2023xgo: Helium-rich Type Icn or Carbon-Flash Type Ibn supernova? Monthly Notices of the Royal Astronomical Society. ISSN 0035-8711 (Accepted)

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Abstract

We present observations of SN 2023xgo, a transitional Type Ibn/Icn SN, from −5.6 to 63 days relative to r-band peak. Early spectra show C iii λ5696 emission like Type Icn SNe, shifting to Type Ibn features. The He i velocities (1800-10000 km s−1) and pseudo-equivalent widths are among the highest in the Ibn/Icn class. The light curve declines at 0.14mag d−1 until 30 days, matching SNe Ibn/Icn but slower than fast transients. SN 2023xgo is the faintest in our SN Ibn sample (Mr = −17.65 ± 0.04) but shows typical colour and host properties. Semi-analytical modelling of the light curve suggests a compact CSM shell (∼1012 − 1013 cm), mass-loss rate between 10−4 − 10−3 M⊙ yr−1 with CSM and ejecta masses of ∼0.22 and 0.12 M⊙, respectively. Post-maximum light-curve, spectral modelling favours a ∼3 M⊙ helium star progenitor with extended (∼1015 cm), stratified CSM (density exponent of 2.9) and mass-loss rate of 0.1 − 2.7 M⊙ yr−1. These two mass-loss regimes imply a radially varying CSM, shaped by asymmetry or changes in the progenitor's mass loss over time. This mass-loss behavior fits both binary and single-star evolution. Early Icn-like features stem from hot carbon ionization, fading to Ibn-like with cooling. SN 2023xgo thus offers rare insight into the connection between SNe Icn, Ibn, and SNe Ibn with ejecta signatures

Item Type:	Article
Additional Information:	This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Press.
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	10 September 2025
Date of first compliant Open Access:	6 November 2025
Date Deposited:	06 Nov 2025 15:28
Last Modified:	06 Nov 2025 15:45
DOI or ID number:	10.1093/mnras/staf1517
URI:	https://researchonline.ljmu.ac.uk/id/eprint/27512

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