EP250108a/SN 2025kg: A Jet-driven Stellar Explosion Interacting with Circumstellar Material

Srinivasaragavan, GP ORCID: 0000-0002-6428-2700, Hamidani, H ORCID: 0000-0003-2866-4522, Schroeder, G ORCID: 0000-0001-9915-8147, Sarin, N ORCID: 0000-0003-2700-1030, Ho, AYQ ORCID: 0000-0002-9017-3567, Piro, AL ORCID: 0000-0001-6806-0673, Cenko, SB ORCID: 0000-0003-1673-970X, Anand, S ORCID: 0000-0003-3768-7515, Sollerman, J ORCID: 0000-0003-1546-6615, Perley, DA ORCID: 0000-0001-8472-1996, Maeda, K ORCID: 0000-0003-2611-7269, O’Connor, B ORCID: 0000-0002-9700-0036, Kuncarayakti, H ORCID: 0000-0002-1132-1366, Miller, MC ORCID: 0000-0002-2666-728X, Ahumada, T ORCID: 0000-0002-2184-6430, Vail, JL ORCID: 0009-0000-4044-8799, Duffell, P ORCID: 0000-0001-7626-9629, Dastidar, R ORCID: 0009-0000-6548-6177, Andreoni, I ORCID: 0000-0002-8977-1498, Bochenek, A ORCID: 0009-0008-2714-2507 et al (2025) EP250108a/SN 2025kg: A Jet-driven Stellar Explosion Interacting with Circumstellar Material. The Astrophysical Journal Letters, 988 (2). ISSN 2041-8205

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Abstract

We present optical, radio, and X-ray observations of EP250108a/SN 2025kg, a broad-line Type Ic supernova (SN Ic-BL) accompanying an Einstein Probe (EP) fast X-ray transient at z = 0.176. EP250108a/SN 2025kg possesses a double-peaked optical light curve, and its spectrum transitions from a blue underlying continuum to a typical SN Ic-BL spectrum over time. We fit a radioactive decay model to the second peak of the optical light curve and find SN parameters that are consistent with the SN Ic-BL population, while its X-ray and radio properties are consistent with those of low-luminosity GRB (LLGRB) 060218/SN 2006aj. We explore three scenarios to understand the system’s multiwavelength emission: (a) SN ejecta interacting with an extended circumstellar medium (CSM), (b) the shocked cocoon of a collapsar-driven jet choked in its stellar envelope, and (c) the shocked cocoon of a collapsar-driven jet choked in an extended CSM. Models (b) and (c) can explain the optical light curve and are also consistent with the radio and X-ray observations. We favor model (c) because it can self-consistently explain both the X-ray prompt emission and first optical peak, but we do not rule out model (b). From the properties of the first peak in model (c), we find evidence that EP250108a/SN 2025kg interacts with an extended CSM and infer an envelope mass Me ∼ 0.1 M⊙ and radius Re ∼ 4 × 1013 cm. EP250108a/SN 2025kg’s multiwavelength properties make it a close analog to LLGRB 060218/SN 2006aj and highlight the power of early follow-up observations in mapping the environments of massive stars prior to core collapse.

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	25 June 2025
Date of first compliant Open Access:	1 August 2025
Date Deposited:	01 Aug 2025 15:50
Last Modified:	01 Aug 2025 16:00
DOI or ID number:	10.3847/2041-8213/ade870
URI:	https://researchonline.ljmu.ac.uk/id/eprint/26887

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