The Type IIn SN 2025cbj coincidence with the high-energy neutrino IceCube-250421A

Garrappa, S, Zimmerman, EA, Wasserman, T, Ofek, EO, Gal-Yam, A, Konno, R, Chen, P, Yaron, O, Ben-Ami, S, Copperwheat, CM ORCID: 0000-0001-7983-8698, Fainer, S, Horowicz, A, Humpe, A, Mazzali, PA, Polishook, D, Segre, E and Spitzer, SA (2026) The Type IIn SN 2025cbj coincidence with the high-energy neutrino IceCube-250421A. Astronomy & Astrophysics, 708. ISSN 0004-6361

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Abstract

Context. The origins of astrophysical high-energy neutrino flux remain uncertain. Core-collapse supernovae (CCSNe) with strong circumstellar material (CSM) interactions (i.e., Type IIn, a.k.a. SNe IIn) are compelling candidates for explaining efficient hadronic acceleration and neutrino production.

Aims. We investigate the possible association between the SNe IIn SN2025cbj and the IceCube high-energy neutrino IceCube-250421A. We assess whether the observed properties of the SN would enable an appreciable neutrino yield.

Methods. We combined rapid optical follow-ups with LAST and archival ZTF photometry with spectroscopy from LT/SPRAT and MMT/BINOSPEC to characterize the SN’s evolution and CSM interaction. We estimated the explosion and peak times from an early light-curve fitting and quantified the chance-coincidence probability with resampling simulations that scramble neutrino right ascensions, while preserving declinations and error contours. Using a simple post-shock-breakout interaction model in a dense wind, we estimated the expected muon-neutrino yield for IceCube’s real-time Bronze stream.

Results. The spectra of SN2025cbj obtained after the neutrino epoch exhibit persistent narrow Balmer lines superposed on broad Lorentzian electron-scattering wings, consistent with a sustained dense CSM interaction. For the multimessenger association, resampling the simulations against the TNS catalog gives a chance-coincidence p-value of p ≃ 0.24 for observing k ≥ 1 events (and p ≃ 0.078 against the ZTF-BTS catalog). These values are sensitive to the size of the SN and neutrino samples and do not indicate a statistically significant multimessenger association. A post-breakout interaction scenario predicts an expected Nνμ ∼ 10−3 events in the IceCube Bronze alert stream over 96 days per this one candidate. We discuss the implications of these numbers and the possible biases that could affect these results.

Item Type:	Article
Uncontrolled Keywords:	astro-ph.HE; astro-ph.HE; 5106 Nuclear and Plasma Physics; 5107 Particle and High Energy Physics; 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:	EDP Sciences
Date of acceptance:	12 February 2026
Date of first compliant Open Access:	20 April 2026
Date Deposited:	20 Apr 2026 14:51
Last Modified:	20 Apr 2026 14:51
DOI or ID number:	10.1051/0004-6361/202558356
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28414

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