GCN Circular 45629

B.Zhang, J. P. Feng (USTC), G. Y. Zhao (QTNU), Z.-C. Zou (NJU), W. D. Zhang (NAO,CAS) on behalf of the Einstein Probe (EP) team: 

We report on the detection of a fast X-ray transient, designated EP260917b, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was independently detected by two CMOS detectors during an observation starting from 2026-09-17T15:28:53 (UTC), and identified by ground-based telemetry analysis. The WXT position of the source is R.A. = 281.628 deg, DEC = -17.562 deg (J2000) with an uncertainty of 2.636 arcmin in radius (90% C.L. statistical and systematic). No flaring activity or strong variability is seen in its lightcurve. No cataloged X-ray sources have been found within the WXT error circle. 

The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 1.61×10^21 cm^-2 and a photon index of -0.27 (-0.63/+0.57). The derived average unabsorbed 0.5-4 keV flux is 1.31 (-0.37/+0.44) × 10^-10 erg cm^-2 s^-1. All uncertainties are reported in 90% C.L.
 
We have arranged a follow-up observation with the Follow-up X-ray Telescope onboard EP and will update the information upon receiving the data. Multi-wavelength observations are strongly encouraged.

Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).