TITLE:   GCN CIRCULAR
NUMBER:  37967
SUBJECT: EP241026b: EP-FXT follow-up observation
DATE:    24/10/30 13:14:26 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

T.Y. Lian, Y. L. Wang, D. Y. Li, S. X. Wen, W. Yuan (NAO, CAS) on behalf of the Einstein Probe team 

Following the detection of the fast X-ray transient EP241026b (Lian et al., GCN 37902), we performed an observation of EP241026b with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe. The observation started at 2024-10-27T03:36:23 (UTC), about 9 hours after the EP-WXT detection, with an exposure time of 4037 seconds. An uncatalogued X-ray source is detected at R.A. = 56.4058 deg, DEC = 41.0312 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average FXT spectrum in 0.5-10 keV band can be fitted by an absorbed power law with a photon index of 2.3(+1.5/-1.4) (with a column density fixed at the Galactic one of 3.38 x 10^21 cm^-2), giving an average unabsorbed flux of 1.5(+2.8/-0.5) x 10^-13 erg/s/cm^2 in the 0.5-10 keV band. The FXT position is 2 arcsec away from the likely optical counterpart detected by LBT (Rossi et al., GCN 37938). We thus consider that the FXT detection is the X-ray counterpart of EP241026b. 

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).