TITLE:   GCN CIRCULAR
NUMBER:  37836
SUBJECT: GRB 241018A: EP-FXT afterglow detection
DATE:    24/10/22 08:58:02 GMT
FROM:    Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>

D. Turpin (CEA), Q. Y. Wu, H. N. Yang, J. W. Hu, H. W. Pan, W. Yuan (NAOC, CAS), C. Plasse, D. Adrien (CEA/irfu), J. Guan, C. K. Li, Y . Chen, S. M. Jia, W. W. Cui, D. W. Han, W. Li, C. Z. Liu, F . J. Lu, L. M. Song, J. Wang, J. J. Xu, J. Zhang, S. N. Zhang, H. S. Zhao, X. F . Zhao (IHEP , CAS), Y . Liu, C. C. Jin, C. Zhang, Z. X. Ling, J. Wang, L. P . Xin (NAOC,CAS), E. Kuulkers, A. Santovincenzo (ESA), P . O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the SVOM and Einstein Probe teams

We performed a follow-up observation of GRB 241018A (Atteia et al., GCN 37812)  with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2024-10-18T20:47:29.912 (T-TGRB ~ 9hr) for about 3ks of exposure in total. 

An uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000)
RA, DEC = 67.9992, 43.0200 (error=10", 90% C.L.), 43.4 arscecond away from the SVOM/ECLAIRs position (Atteia et al., GCN 37812). This position is also consistent with the optical afterglow detected by SVOM/VT (Qiu et al., GCN 37819, GCN 37826) and the NOT (Malesani et al., GCN 37821) as well as the X-ray counterpart detected by Swift/XRT (Osborne et al., GCN 37823). 

A preliminary analysis shows that the spectrum can be fitted with an absorbed powerlaw with nH=9.5(-5.7/+6.9)*10^21 cm^-2 and photon index of 2.5 (-1.1/+1.2) . The observed flux in the 0.5-10.0 keV is 1.8(-0.7/+1.6)*10^-13 erg/s/cm^2.
 
The above observation was made with the EP-FXT instrument. 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.