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GCN Circular 37230

Subject
GRB 240821A: EP-FXT follow-up observation and afterglow candidates
Date
2024-08-22T13:59:09Z (3 months ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
D. Turpin (CEA), H. Q. Cheng, W. Xie (NAOC, CAS), Y. F. Liang (PMO, CAS), J. Q. Peng (IHEP, CAS), W. Yuan (NAOC, CAS), S. Guillot (IRAP), 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), H. Sun, Y. Liu, C. C. Jin, C. Zhang, 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 240821A (detected by SVOM/ECLAIRs Cangemi et al, GCN 37220Not found
 
 
; SVOM/GRM He et al. GCN 37226Not found
 
 
 and Fermi/GBM GCN 37219Not found
 
 
) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation began at 2024-08-22T03:22:05 (T-TGRB ~ 9 hrs), and the exposure time is about 3.0 ks. FXT-A detected 2 uncatalogued sources in the 90% localization error circle provided by SVOM/ECLAIRs (with a radius of 13 arcmin centered at RA, DEC = 354.23 deg, -10.18 deg), and 7 are detected by FXT-B.

The following table lists the detailed information of the X-ray sources detected by FXT-A and FXT-B. The positions are given with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The uncertainties of flux are at the 90% confidence level.

FXT-A candidate list: 
Source name         | RA       |  DEC     | Estimated Flux       | SNR | Dist from SVOM/ECLAIRs |
                    | deg      |  deg     | (erg/s/cm^2)         |     | offset (in arcmin)     |
-------------------------------------------------------------------------------------------------
EP J233704.9-101126 | 354.2703 | -10.1905 | 1.3(+/-0.3) x 10^-13 | 7.6 |          2.46          | 
EP J233641.3-100257 | 354.1720 | -10.0491 | 5.5(+/-2.2) x 10^-14 | 4.2 |          8.57          | 
-------------------------------------------------------------------------------------------------

FXT-B candidate list: 
Source name         | RA       |  DEC     | Estimated Flux       | SNR | Dist from SVOM/ECLAIRs |
                    | deg      |  deg     | (erg/s/cm^2)         |     | offset (in arcmin)     |
-------------------------------------------------------------------------------------------------                    
EP J233704.9-101126 | 354.2696 | -10.1893 | 1.2(+/-0.3) x 10^-13 | 8.5 |          2.40          | 
EP J233641.6-101036 | 354.1735 | -10.1767 | 7.5(+/-2.2) x 10^-14 | 5.1 |          3.34          | 
EP J233642.1-101318 | 354.1754 | -10.2217 | 5.9(+/-2.0) x 10^-14 | 3.8 |          4.08          | 
EP J233708.1-101515 | 354.2836 | -10.2542 | 3.0(+/-1.3) x 10^-14 | 4.3 |          5.46          | 
EP J233710.3-100324 | 354.2929 | -10.0566 | 8.4(+/-3.0) x 10^-14 | 3.9 |          8.28          | 
EP J233727.8-100744 | 354.3657 | -10.1290 | 4.0(+/-1.6) x 10^-14 | 4.6 |          8.58          | 
EP J233636.5-100302 | 354.1522 | -10.0507 | 7.8(+/-2.2) x 10^-14 | 6.3 |          9.02          | 
-------------------------------------------------------------------------------------------------

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.