GCN Circular 45621
Subject
EP260917a: Einstein Probe detection of an X-ray transient
Event
Date
2026-09-18T05:31:07Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Q.J. Huang (PMO, CAS), K. R. Ni (CCNU), T. Wu (AHNU), H. W. Pan (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 EP260917a. The transient triggered EP-WXT (ID: 01709318047) at 2026-09-17T09:37:45 (UTC). The WXT position of the source is R.A. = 335.151 deg, DEC = 9.481 deg (J2000) with an uncertainty of 1.986 arcmin in radius (90% C.L. statistical and systematic).
The refined analysis of the WXT data shows that the event started at T0=2026-09-17T09:32:07 (UTC), and lasted for approximately 1500 seconds, after which the observation was interrupted due to Earth occultation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 5.08 (-1.73/+2.05) × 10^21 cm^-2, and a photon index of 2.31 (-0.65/+0.77). The derived average unabsorbed 0.5-4 keV flux is 5.55 (-0.98/+2.04) × 10^(-10) erg/s/cm^2, with a peak flux of about 2.06 × 10^(-9) erg/s/cm^2.
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).