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

Résumé fourni par la source

Abstract 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 ∼10 45 erg s −1 , lasts over 1000 s, and has a peak energy E p < 1.5 keV at 90% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for ∼20 days, consistent with a central engine injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted broad absorption features consistent with a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet ≳10 50 erg assuming a typical LGRB circumburst constant density ( n ≈ 10 −3 –10 −1 cm −3 ) and microphysical parameters ( ϵ e = 0.1 and ϵ B = 0.01). 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 ∼0.35 c and interact with an extended circumstellar medium with radius ∼10 13 cm, generating X-ray breakout emission through nonthermal free–free processes. The disk outflows and magnetar winds power blackbody photospheric emission as they cool adiabatically and thermalize, producing the first SN peak. The spin-down luminosity of the magnetar and radioactive decay of 56 Ni power the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP’s recent discoveries.

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