TITLE: GCN CIRCULAR NUMBER: 38632 SUBJECT: GRB 241209B: EP-FXT afterglow detection DATE: 24/12/19 09:28:48 GMT FROM: Damien Turpin at CEA-Saclay dturpin-astro@hotmail.com
D. Turpin (CEA), Y. L. Wang, T. Zhao, M. J. Liu (NAOC, CAS), Z. Y. Liu, M. Q. Huang (USTC), H. W. Pan, W. Yuan (NAOC, CAS), D. Adrien, C. Plasse (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 241209B (SVOM/ECLAIRs and GRM, Xie et al., GCN 38478) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2024-12-09T16:01:19 (T-TGRB ~ 12.1hr) for about 3ks of exposure in total and a second epoch was also performed at 2024-12-12T22:35:16 (T-TGRB ~ 3.8 days) for again about 3ks of exposure in total.
In the first epoch, an uncatalogued X-ray source is detected by both FXT-A and FXT-B at the position (J2000) RA, DEC = 194.6388, 76.1747 (error=10", 90% C.L.), 5.75 arcminute away from the SVOM/ECLAIRs position (Xie et al., GCN 38478). This position is also consistent with the optical afterglow detected by SVOM/VT (Qiu et al., GCN 38516, GCN 38568) and Swift/XRT source 1 (Williams et al., GCN 38525).
This source is no longer detected in the second epoch 3.8 days post GRB trigger time confirming it has significantly faded and is indeed the x-ray afterglow of GRB 241209B.
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.
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