TITLE:   GCN CIRCULAR
NUMBER:  37608
SUBJECT: EP240918b and EP240918c: EP-FXT follow-up observations
DATE:    24/09/25 11:33:40 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

M. J. Liu (NAOC ,CAS), Y. F. Liang (PMO, CAS), Z. J. Zhang (HKU), X. P. Xu, C. C. Jin, Z. X. Ling, W. M. Yuan, Y. Liu, C. Zhang, W. Chen, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, Y. F. Xu, H. N. Yang, M. Zhang, W. D. 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 have reported the detection of two fast X-ray transients EP240918b and EP240918c by the Einstein Probe (EP) mission (Liang et al. GCN 37555). 

The follow-up observation with the EP-FXT for EP240918b was performed, starting at 2024-09-19T11:25:26 (UTC), about 20 hours after the detection of the source by WXT. No X-ray source was detected within the 3 arcmin radius region around the WXT position of EP240918b.

The follow-up observations with the EP-FXT for EP240918c were performed, starting at 2024-09-19T12:40:28 (UTC) and 2024-09-24T13:01:28 (UTC), respectively. Two X-ray sources were detected within the 3 arcmin radius region around the WXT position of EP240918c in each observation. EP J184515.3-131115 is detected at R.A. = 281.3138 deg, DEC = -13.1875 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). EP J184516.2-130819 locates at R.A. = 281.3187 deg, DEC = -13.1371 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic), being consistent with the position of the star TYC 5704-6-1. No rapid dimming was found for two sources.

Further follow-up observations are encouraged to identify the nature of EP240918b and EP240918c.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with onboard X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).