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EP250827b/SN 2025wkm: An X-ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction
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EP250827b/SN 2025wkm: An X-ray Flash-Supernova Powered by a Central Engine and Circumstellar Interaction

Gokul P Srinivasaragavan, Dongyue Li, Xander J Hall, Ore Gottlieb, Genevieve Schroeder, Heyang Liu, Brendan O'Connor, Chichuan Jin, Mansi Kasliwal, Tomás Ahumada, …
ArXiv.org
11 Dec 2025
DOI: https://doi.org/10.48550/arxiv.2512.10239
url
https://doi.org/10.48550/arXiv.2512.10239View
Preprint (Author's original) Open arXiv.org - Non-exclusive license to distribute

Abstract

High Energy Astrophysics
We present the discovery of EP250827b/SN 2025wkm, an X-ray Flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at$z = 0.1194$ . EP250827b possesses a prompt X-ray luminosity of$\sim 10^{45} \, \rm{erg \, s^{-1}}$ , lasts over 1000 seconds, and has a peak energy$E_{\rm{p}} < 1.5$keV at 90% confidence. SN 2025wkm possesses a double-peaked light curve (LC), though its bolometric luminosity plateaus after its initial peak for$\sim 20$days, giving evidence that a central engine is injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted Fe II and Si II broad absorption features, allowing for a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet$\gtrsim 10^{50}~$ erg. In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically-driven winds from the magnetar and the disk mix together, and break out with a velocity$\sim 0.35c$from an extended circumstellar medium with radius$\sim 10^{13}$cm, generating X-ray breakout emission through free-free processes. The disk outflows and magnetar winds power blackbody emission as they cool, producing the first peak in the SN LC. The spin-down luminosity of the magnetar in combination with the radioactive decay of$^{56}$ Ni produces the late-time SN LC. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries.

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