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

August 2026 • 2026ApJ..1006L..36S

Authors • Srinivasaragavan, Gokul P. • Li, Dongyue • Hall, Xander J. • Gottlieb, Ore • Schroeder, Genevieve • Liu, Heyang • O'Connor, Brendan • Jin, Chichuan • Kasliwal, Mansi • Ahumada, Tomás • Wu, Qinyu • Fryer, Christopher L. • Niblett, Annabelle E. • Xu, Dong • Ravasio, Maria Edvige • Daja, Grace • Li, Wenxiong • Anand, Shreya • Ho, Anna Y. Q. • Sun, Hui • Perley, Daniel A. • Yan, Lin • Burns, Eric • Cenko, S. Bradley • Sollerman, Jesper • Sarin, Nikhil • Piro, Anthony L. • Aryan, Amar • Miller, M. Coleman • An, Jie • An, Tao • Andrews, Moira • Augustin, Jule • Bellm, Eric C. • Bochenek, Aleksandra • Busmann, Malte • Chanchaiworawit, Krittapas • Cheng, Huaqing • Caballero-García, Maria D. • Castro-Tirado, Alberto J. • Esamdin, Ali • Fabá-Moreno, Jennifer • Farah, Joseph • Fernández-García, Emilio • Fu, Shaoyu • Fynbo, Johan P. U. • Gassert, Julius • Padilla Gonzalez, Estefania • Pérez-García, Ignacio • Graham, Matthew • Gritsevich, Maria • Gruen, Daniel • Guziy, Sergiy • He, Linbo • Howell, D. Andrew • Hu, Jingwei • Hu, You-Dong • Iskandar, Abdusamatjan • Jaimes, Joahan Castaneda • Jiang, Ji-An • Jiang, Ning • Jiang, Shuaiqing • Liang, Runduo • Ling, Zhixing • Liu, Jialian • Liu, Xing • Liu, Yuan • Masci, Frank J. • McCully, Curtis • Newsome, Megan • Noysena, Kanthanakorn • Pandey, Shashi B. • Ni, Kangrui • Palmese, Antonella • Peng, Han-Long • Purdum, Josiah • Qin, Yu-Jing • Rose, Sam • Rusholme, Ben • Sánchez-Ramírez, Rubén • Sevilla, Cassie • Smith, Roger • Song, Yujia • Sravan, Niharika • Stein, Robert • Tabor, Constantin • Terreran, Giacomo • Tinyanont, Samaporn • Vega, Pablo • Wang, Letian • Waing, Tinggui • Wang, Xiaofeng • Wu, Siyu • Wu, Xuefeng • Wynn, Kathryn • Xu, Yunfei • Yan, Shengyu • Yuan, Weimin • Zhang, Binbin • Zhang, Chen • Zhu, Zipei • Zuo, Xiaoxiong • Bhullar, Gursimran

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 ∼10⁴⁵ 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 ≳10⁵⁰ 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 ∼0.35c and interact with an extended circumstellar medium with radius ∼10¹³ 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 ⁵⁶Ni power the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP's recent discoveries.

Links

• ELECTR https://doi.org/10.3847/2041-8213/ae7a68
• PREPRINT http://arxiv.org/abs/2512.10239