{
  "format": "text/plain",
  "body": "M. J. Liu, Q. Y. Wu, T. Zhao, Y. J. Song (NAO, CAS), H. Z. Wu (HUST), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:\n\nWe report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250428b (GCN Notice ID 01799135422). The WXT position of the source is R.A. = 220.479 deg, DEC = 2.09 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). A preliminary analysis of the EP-WXT data shows that the transient began at around 2025-04-28T06:05:31(UTC) and lasted for a few hundreds of seconds, with a peak flux of around 3 x 10^-10 erg/cm^2/s. The averaged WXT spectrum can be fitted by an absorbed power law model with a Galactic hydrogen column density of 3.77 x 10^20 cm^-2 and a photon index of 1.9 (+0.2, -0.2). The averaged unabsorbed 0.5-4 keV flux is 3.3 (+2.2, -1.3) x 10^-11 erg/cm^2/s. The uncertainties are at the 90% confidence level for the above parameters.\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) was performed from 2025-04-29T13:41:27 (UTC). Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 220.4586 deg, DEC = 2.1002 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received.\n\nThe contact TA of EP250428b is Q. Y. Wu. Please contact him via email qywu@bao.ac.cn if needed.\n\nLaunched 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).",
  "circularId": 40277,
  "bibcode": "2025GCN.40277....1L",
  "createdOn": 1745947836611,
  "subject": "EP250428b: Einstein Probe detection of a fast X-ray transient",
  "submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
  "submittedHow": "web",
  "eventId": "EP250428b"
}