TITLE: GCN CIRCULAR NUMBER: 44766 SUBJECT: EP260601a: Einstein Probe detection of an X-ray transient DATE: 26/06/02 11:52:06 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> G. J. Yang (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260601a. The transient triggered EP-WXT (ID: 01709266307) at 2026-06-01T19:13:22 UTC. The WXT position of the source is R.A. = 257.649 deg, Dec = -1.647 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The preliminary analysis of the WXT data shows that the burst started at T_0 = 2026-06-01T19:12:41 UTC. The light curve shows an initial flare lasting approximately 100 s, followed by tail emission. During the flare, the unabsorbed 0.5-4 keV flux was 5.2 (-1.7/+3.6) x 10^-08 erg cm^-2 s^-1. The time-averaged WXT 0.5-4 keV spectrum over the entire detected emission can be described by an absorbed power law, with the hydrogen column density left as a free parameter. The best-fit hydrogen column density is 6.7 (-1.5/+1.6) x 10^21 cm^-2. The best-fit photon index is 1.2 (-0.3/+0.3). The unabsorbed 0.5-4 keV flux is 2.4 (-0.2/+0.3) x 10^-10 erg cm^-2 s^-1. A follow-up observation with the Follow-up X-ray Telescope (FXT) onboard EP is scheduled. Further information will be updated when the telemetry data is received. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/44766. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...