GCN Circular 46025

G. J. Yang (NAO, CAS), S. Q. Zheng, J. R. Liu (BNU), Q. Y. Wu and Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team:

We report the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP261025a. The EP-WXT observation (ID: 08500000682) started at 2026-10-25T05:38:04 UTC, with an exposure time of 5605 s. The WXT light curve of the transient began at 2026-10-25T07:19:57.4 UTC and lasted for ~130 s. The WXT position of the source is R.A. = 2.554 deg, DEC = 60.763 deg (J2000) (l=117.917 deg, b=-1.707 deg) with an uncertainty of 2.22 arcmin in radius (90% C.L. statistical and systematic).

We fitted the WXT spectrum with an absorbed power-law model, fixing nH at the Galactic value 7.06e21 cm-2. We obtained a photon index of 1.6(-0.3/+0.3) and an unabsorbed flux of 2.6(-0.3/+0.3)e-9 erg/cm2/s during the flare. 

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed at 2026-10-25T13:13:55. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 2.5488 deg, DEC = 60.7658 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. Multi-wavelength observations are encouraged. 

Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.