TITLE: GCN CIRCULAR NUMBER: 39224 SUBJECT: EP250207a: EP-WXT detection and XRT follow-up observation DATE: 25/02/08 05:14:40 GMT FROM: EP Team at NAOC/CAS D. Y. Li, M. J. Liu, J. An, S.Y. Fu, S. Q. Jiang, X. Liu, D. Xu, Z. P. Zhu, M. H. Zhang (NAOC, CAS), Q. C. Shui (IHEP, CAS), W. D. Zhang (NAOC, CAS) report on behalf of the Einstein Probe team: We report on the detection of an X-ray transient by EP-WXT, designated EP250207a, which triggered the on-board processing unit at 2025-02-07T15:51:17 (trigger ID: 01709131361). The WXT position of the source is R.A. = 356.902 deg, DEC = 27.027 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). The average 0.5-4 keV spectrum can be fitted with an apec model with a temperature of 3.1 (-1.2, +5.9) keV. No significant absorption is required during the spectral fitting. The derived average 0.5-4 keV flux is 2.9 (-0.7, +0.9) x10^-10 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. We performed a target of opportunity observation with Swift. The Swift XRT observation began at 2025-02-07T17:59:50 (UTC) with an exposure time of 1716 seconds in the Photon Counting mode, about 2 hours after the burst detected by EP-WXT. A bright X-ray source, which is spatially consistent with the low-mass star 2MASS J23473680+2702068 (distance ~ 21.3 pc), was detected within the WXT error circle. The X-ray spectrum can be fitted with two apec components, with temperature of 0.75 (-0.3, +0.2) keV, and 2.6 (-0.6, +1.3) keV, respevtively. No significant absorption is required during the spectral fitting. The derived 0.3-10 keV flux is 9.2 (-1.0, +1.1)x10^-12 erg/s/cm2, corresponding to a luminosity of around 5x10^29 erg/s. We suggest this transient is a stellar flare from this low-mass star. We thank the Neil Gehrels Swift team for making the quick follow-up observation possible. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).