TITLE: GCN CIRCULAR NUMBER: 38726 SUBJECT: GRB 241229A: EP-FXT afterglow candidates DATE: 24/12/30 11:41:58 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

S.Q. Jiang, J. W. Hu, W. J. Zhang, X.P. Xu (NAO, CAS), W.F. Wen (SZTU), J. H. Wu (GU), H.W. Pan, Z.X. Ling (NAO, CAS), B. Cordier (CEA) on behalf of Einstein Probe teams:

We performed a follow-up observation of GRB 241229A (SVOM/ECLAIRs, Liang et al., GCN 38697) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started at 2024-12-29 14:11:35 (T-TGRB ~ 14.1 hr) for about 3 ks of exposure in total.

Three uncatalogued X-ray sources are detected by both FXT-A and FXT-B within the 7.6 arcmin error circle of SVOM/ECLAIRs (Liang et al., GCN 38697). We list the sources in the following table, with the seperations from the ECLAIRs source given. The observed 0.5-10 keV flux given in the table is a rough estimate assuming the same spectral paramters, and is not corrected for absorption.

| FXT source | R.A. (deg, J2000) | DEC (deg, J2000) | Sep. (arcmin) | Flux (erg/s/cm^2) | | EPF_J125139.4+315311  | 192.9133 | 31.8867 | 2.06 | 6.82 x 10^(-14) | | EPF_J125129.3+314453* | 192.8715 | 31.7484 | 6.61 | 7.73 x 10^(-13) | | EPF_J125101.6+315007  |  192.7572 | 31.8356 | 7.04 | 9.25 x 10^(-14) | * sources also detected by Swift/XRT (Evans et al., GCN 38711)

Further follow-up observation will be performed by the EP-FXT to confirm the afterglow of GRB 241229A.

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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