GCN Circular 37088

Y. C. Fu (BNU), S. Q. Jiang, J. W. Hu, Z. X. Ling, W. D. Zhang, Y. Liu, 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, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, 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 EP240807a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2024-08-07T05:42:48(UTC). The WXT position of EP240807a is R.A.= 300.970 deg, DEC = -68.777 deg (J2000) with an uncertainty of 2.5 arcmin (radius, 90% C.L. statistical and systematic). The lightcurve of the transient observed by the WXT lasts around 70 seconds and has a peak flux of ~1 x 10^-8 erg/s/cm^2 in the 0.5-4 keV band. The average 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 0.9(-0.8, +1.7) (with a freely fitted column density value of 1.1(-1.1, +1.6) x 10^21 cm^-2). The derived average unabsorbed 0.5-4 keV flux is 1.7(-0.6, +0.7) x 10^(-10) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.

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).