Rastinejad, Jillian C. and Levan, Andrew J. and Jonker, Peter G. and Kilpatrick, Charles D. and Fryer, Christopher L. and Sarin, Nikhil and Gompertz, Benjamin P. and Liu, Chang and Eyles-Ferris, Rob A. J. and Fong, Wen-fai and Burns, Eric and Gillanders, James H. and Mandel, Ilya and Malesani, Daniele Bjørn and O’Brien, Paul T. and Tanvir, Nial R. and Ackley, Kendall and Aryan, Amar and Bauer, Franz E. and Bloemen, Steven and de Boer, Thomas and Bom, Clécio R. and Chacón, Jennifer A. and Chambers, Ken and Chen, Ting-Wan and Chrimes, Ashley A. and van Dalen, Joyce N. D. and D’Elia, Valerio and De Pasquale, Massimiliano and Fulton, Michael D. and Groot, Paul J. and Gupta, Rahul and Hartmann, Dieter H. and van Hoof, Agnes P. C. and Huber, Mark E. and Izzo, Luca and Jacobson-Galan, Wynn and Jakobsson, Páll and Kong, Albert and Laskar, Tanmoy and Lowe, Thomas B. and Magnier, Eugene A. and Maiorano, Elisabetta and Martin-Carrillo, Antonio and Mas-Ribas, Lluis and Mata Sánchez, Daniel and Nicholl, Matt and Nixon, Christopher J. and Oates, Samantha R. and Paek, Gregory and Palmerio, Jesse and Paris, Diego and Pieterse, Daniëlle L. A. and Pugliese, Giovanna and Vasquez, Jonathan A. Quirola and van Roestel, Jan and Rossi, Andrea and Rouco Escorial, Alicia and Salvaterra, Ruben and Schneider, Benjamin and Smartt, Stephen J. and Smith, Ken and Smith, Ian A. and Srivastav, Shubham and Torres, Manuel A. P. and Ventura, Chiara and Vreeswijk, Paul and Wainscoat, Richard and Yang, Yi-Jung and Yang, Sheng (2025) EP 250108a/SN 2025kg : Observations of the Most Nearby Broad-line Type Ic Supernova Following an Einstein Probe Fast X-Ray Transient. Astrophysical Journal Letters, 988 (1): L13. ISSN 2041-8205
Full text not available from this repository.Abstract
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.