TITLE:   GCN CIRCULAR
NUMBER:  37063
SUBJECT: EP240806a: EP-WXT detection of a fast X-ray transient
DATE:    24/08/06 10:15:25 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

Q. Y. Wu (NAOC, CAS), Y. J. Zhang (THU), Y. Wang (PMO, CAS), H. Sun, Y. L. Wang, W. D. Zhang, Y. Liu, H. W. Pan, Z. X. Ling, C. C. Jin, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, X. Pan, W. X. Wang, Y. L. Wang, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, W. W. Cui, D. W. Han, C. K. Li, L. M. Song, X. F. Zhao, J. Zhang, 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 fast X-ray transient designated EP240806a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2024-08-06T04:47:53.9(UTC) and triggered the WXT on-board processing unit (trigger ID: 01709017970). The WXT position of EP240806a is R.A.= 11.491 deg, DEC = 5.091 deg (J2000) with an uncertainty of 2.1 arcmin (radius, 90% C.L. statistical and systematic). The lightcurve of the transient observed by the WXT lasts around 150 seconds. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 2.6(-1.0, +1.2) (with a freely fitted column density value of 3.1(-2.5, +2.8) x 10^21 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.9(-0.6, +1.8) x 10^(-9) erg/s/cm^2. 

No previously known bright X-ray sources are found within the error circle around the source position. Following the WXT detection, we performed a follow-up observation with the Follow-up X-ray Telescope (FXT) on board the EP. Further follow-up observations are encouraged to identify the nature of this X-ray transient. 
 
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).