GCN Circular 36512

Q.Y. Wu (NAOC, CAS), A. Li (BNU), Y. Liu, W. Yuan, Z. X. Ling, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang (NAOC,CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team 
 
We report on the detection of a new X-ray transient, designated EP240518a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission during a calibration observation. The transient triggered the WXT on-board processing unit at 2024-05-18T13:01:50 (UTC). The position of the source is R.A. = 216.955 deg, DEC = -49.565 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for more than 1000 seconds and has an average flux of 8 x 10^-11 erg/s/cm^2 in the 0.5-4 keV band.
 
No previously known X-ray sources at a similar flux level are found within the 3 arcmin region around the source position. More information will be provided once the data has been transmitted through a ground station. Further multi-wavelength follow-up observations are encouraged to identify the nature of this X-ray flare.
 
The above observation was made with the WXT instrument during the commissioning phase of EP. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.