SN 2018erx: A Fast-evolving, Dust-reddened Type Icn Supernova with Broad C II Emission Lines

October 2026 • 2026PASP..138j4206D

Authors • Das, Kaustav K. • Gangopadhyay, Anjasha • Kasliwal, Mansi M. • Sollerman, Jesper • Perley, Daniel A. • Schulze, Steve • Fremling, Christoffer • Coughlin, Michael W. • De, Kishalay • Gal-Yam, Avishay • Goobar, Ariel • Graham, Matthew • Masci, Frank J. • Moriya, Takashi J. • Purdum, Josiah • Rose, Sam • Rusholme, Ben • Sarin, Nikhil • Smith, Roger • Tsuna, Daichi

Abstract • We present the discovery and characterization of SN 2018erx (ZTF18abkmbpy), a fast-evolving, unusually red, interacting stripped-envelope supernova. Spectroscopically, SN 2018erx exhibits prominent broad C II emission with characteristic widths of ~3800 km s^-1, consistent with interaction with a carbon-rich circumstellar medium (CSM) and a Type Icn core-collapse SN classification. Photometrically, SN 2018erx evolves exceptionally rapidly, rising from half-maximum to peak in 2.1 days and declining back in 3.1 days, placing it among the fastest-evolving core-collapse supernovae observed. Semi-analytical CSM-interaction modeling favors a compact, shell-like CSM with M_CSM ≈ 0.3 M_⊙, an inner radius of R₀ ≈ 0.7 au, and a very low ejecta mass of M_ej ≈ 0.11 M_⊙. The radioactive yield is likewise small, with a ⁵⁶Ni mass ≲(3--5) × 10^-3 M_⊙, placing SN 2018erx at the low end of the H-poor stripped-envelope SN distribution. At +29 days after peak, we detect a near-infrared excess consistent with pre-existing local circumstellar dust and infer a hot-dust mass of M_d ~ 10^-6--10^-5 M_⊙. Taken together, the rapid evolution, strong local reddening, carbon-rich emission, and evidence for pre-existing dust point to a multi-component circumstellar environment consisting of a dense inner interaction region produced by enhanced pre-SN mass loss ( Ṁ~10-4 --10^-3 M_⊙ yr^-1) and an outer dusty layer at R ≳ 4 × 10¹⁶ cm, produced by an earlier mass-loss episode roughly 10--200 yr before core collapse. These properties favor an ultra-stripped core-collapse explosion of a low-mass He star in a binary system that underwent late-time Case BC mass transfer or Si-flash-induced mass loss. Fallback-modified Wolf--Rayet collapse or a merger-driven mass-loss episode remain plausible alternatives. These observations provide rare insight into the mass-loss history of stripped-envelope SNe, indicate that SN 2018erx-like events may be efficient sites of dust formation, and suggest that dust-enshrouded explosions of this kind may be systematically underrepresented in optical surveys.

Links

• PDF https://iopscience.iop.org/article/10.1088/1538-3873/aead22/pdf
• PREPRINT http://arxiv.org/abs/2605.24811
• ELECTR https://doi.org/10.1088/1538-3873/aead22