| Title: |
The Kangaroo’s First Hop: The Early Fast Cooling Phase of EP250108a/SN 2025kg |
| Authors: |
Eyles-Ferris, RAJ; Jonker, PG; Levan, AJ; Malesani, DB; Sarin, N; Fryer, CL; Rastinejad, JC; Burns, E; Tanvir, NR; O’Brien, PT; Fong, W; Mandel, I; Gompertz, BP; Kilpatrick, CD; Bloemen, S; Bright, JS; Carotenuto, F; Corcoran, G; Cotter, L; Groot, PJ; Izzo, L; Laskar, T; Martin-Carrillo, A; Palmerio, J |
| Publisher Information: |
American Astronomical Society |
| Publication Year: |
2025 |
| Collection: |
Oxford University Research Archive (ORA) |
| Description: |
Fast X-ray transients are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its Wide-field X-ray Telescope has led to a rapid expansionof the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart, SN 2025kg, or “the kangaroo.” Together with a companion Letter we present our observing campaign and analysis of this event. In this letter, we focus on the early evolution of the optical counterpart over the first 6 days, including our measurement of the redshift of z = 0.17641. We compare to other supernovae and fast transients showing similar features, finding significant similarities with SN 2006aj and SN 2020bvc, and show that the source is well modelled by a rapidly expanding cooling blackbody. We show the observed X-ray and radio properties are consistent with a collapsar-powered jet that is low energy (≲1051 erg) and/or fails to break out of the dense material surrounding it. While we examine the possibility that the optical emission emerges from the shock produced as the supernova ejecta expand into a dense shell of circumstellar material, due to our X-ray and radio inferences, we favour a model where it arises from a shocked cocoon resulting from a trapped jet. This makes SN 2025 one of the few examples of this currently observationally rare event. |
| Document Type: |
article in journal/newspaper |
| Language: |
English |
| DOI: |
10.3847/2041-8213/ade1d9 |
| Availability: |
https://doi.org/10.3847/2041-8213/ade1d9; https://ora.ox.ac.uk/objects/uuid:08fb52fc-19a0-466a-9a58-1de858fe7b03 |
| Rights: |
info:eu-repo/semantics/openAccess ; CC Attribution (CC BY) |
| Accession Number: |
edsbas.59E29021 |
| Database: |
BASE |