{
  "subject": "EP261015a: Einstein Probe detection of a fast X-ray transient",
  "body": "R.-Z. Li (YNAO), G. -L. Huang, Z.-X. Li (IHEP), M. Nie (YNAO) and H. Sun (NAOC) 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 EP261015a. The transient did not trigger EP-WXT onboard. We sent a GCN Notice manually with trigger ID: 11900947714. The WXT light curve of the transient began at 2026-10-15T13:15:36 UTC, exhibited two peaks, and lasted for 130 s. The WXT position of the source is R.A. = 44.341 deg, DEC = -13.365 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).\n\nThe 0.5-4 keV WXT  spectrum can be fitted by an absorbed powerlaw model with a fixed Galactic column density of 3.5 x 10^20 cm^-2 and a  photon index of 1.45 (-0.71,+0.88). The derived 0.5-4 keV unabsorbed flux is 6.25 (-2.91/+3.90) x 10^-10 erg/cm^2/s.\n\nA follow-up observation with the Follow-up X-ray Telescope (FXT) has been scheduled. Further information will be updated when the telemetry data is received.\n\nA possible optical counterpart to the transient was reported by NOT and LCO (Corcoran et al., GCN 45955).\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).",
  "format": "text/plain",
  "circularId": 45956,
  "eventId": "EP261015a",
  "submittedHow": "web",
  "createdOn": 1792131668685,
  "submitter": "EP Team at NAOC/CAS <ep_ta@bao.ac.cn>",
  "eventType": [
    "X-ray Transient"
  ]
}