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SN 2023xgo: Helium-rich Type Icn or Carbon-Flash Type Ibn supernova?
Journal article   Open access   Peer reviewed

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

Anjasha Gangopadhyay, Jesper Sollerman, Konstantinos Tsalapatas, Keiichi Maeda, Naveen Dukiya, Steve Schulze, Claes Fransson, Nikhil Sarin, Priscila J Pessi, Mridweeka Singh, …
Monthly notices of the Royal Astronomical Society, Forthcoming
10 Sep 2025
DOI: https://doi.org/10.1093/mnras/staf1517
url
https://doi.org/10.1093/mnras/staf1517View
Published, Version of Record (VoR) Open

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.

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