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

Das, KK, Gangopadhyay, A, Kasliwal, MM, Sollerman, J, Perley, DA ORCID: 0000-0001-8472-1996, Schulze, S, Fremling, C, Coughlin, MW, De, K, Gal-Yam, A, Goobar, A, Graham, M, Masci, FJ, Moriya, TJ, Purdum, J, Rose, S, Ben, R, Sarin, N, Smith, R and Tsuna, D (2026) SN 2018erx: A Fast-evolving, Dust-reddened Type Icn Supernova with Broad C II Emission Lines. Publications of the Astronomical Society of the Pacific, 138 (10). ISSN 0004-6280

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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 MCSM ≈ 0.3 M⊙, an inner radius of R0 ≈ 0.7 au, and a very low ejecta mass of Mej ≈ 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 Md ∼ 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 (
–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.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	IOP Publishing
Date of acceptance:	28 September 2026
Date of first compliant Open Access:	5 November 2026
Date Deposited:	05 Nov 2026 13:54
Last Modified:	05 Nov 2026 13:54
DOI or ID number:	10.1088/1538-3873/aead22
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29828

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