| Title: |
EP 250108a/SN 2025kg: Observations of the Most Nearby Broad-line Type Ic Supernova Following an Einstein Probe Fast X-Ray Transient |
| Authors: |
Rastinejad, JC; Levan, AJ; Jonker, PG; Kilpatrick, CD; Fryer, CL; Sarin, N; Gompertz, BP; Liu, C; Eyles-Ferris, RAJ; Fong, W; Burns, E; Gillanders, JH; Mandel, I; Malesani, DB; O’Brien, PT; Tanvir, NR; Ackley, K; Aryan, A; Bauer, FE; Bloemen, S; de Boer, T; Bom, CR; Chacón, JA; Chambers, K; Smartt, SJ; Smith, K; Srivastav, S |
| Publisher Information: |
American Astronomical Society |
| Publication Year: |
2025 |
| Collection: |
Oxford University Research Archive (ORA) |
| Description: |
With a small sample of fast X-ray transients (FXTs) with multiwavelength counterparts discovered to date, their progenitors and connections to γ-ray bursts (GRBs) and supernovae (SNe) remain ambiguous. Here, we present photometric and spectroscopic observations of SN 2025kg, the SN counterpart to the FXT EP 250108a. At z = 0.17641, this is the closest known SN discovered following an Einstein Probe (EP) FXT. We show that SN 2025kg’s optical spectra reveal the hallmark features of a broad-lined Type Ic SN. Its light-curve evolution and expansion velocities are comparable to those of GRB-SNe, including SN 1998bw, and two past FXT-SNe. We present JWST/NIRSpec spectroscopy taken around SN 2025kg’s maximum light, and find weak absorption due to He I 1.0830 μm and 2.0581 μm and a broad, unidentified emission feature at ∼4–4.5 μm. Further, we observe broadened Hα in optical data at 42.5 days that is not detected at other epochs, indicating interaction with H-rich material. From its light curve, we derive a 56Ni mass of 0.2–0.6 M⊙. Together with our companion Letter, our broadband data are consistent with a trapped or low-energy (≲1051 erg) jet-driven explosion from a collapsar with a zero-age main-sequence mass of 15–30 M⊙. Finally, we show that the sample of EP FXT-SNe supports past estimates that low-luminosity jets seen through FXTs are more common than successful (GRB) jets, and that similar FXT-like signatures are likely present in at least a few percent of the brightest Type Ic-BL SNe. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| DOI: |
10.3847/2041-8213/ade7f9 |
| Availability: |
https://doi.org/10.3847/2041-8213/ade7f9; https://ora.ox.ac.uk/objects/uuid:1aa6efd4-9f25-47db-a395-109996649d7a |
| Rights: |
info:eu-repo/semantics/openAccess ; CC Attribution (CC BY) |
| Accession Number: |
edsbas.F7C6A8BE |
| Database: |
BASE |