TITLE: GCN CIRCULAR NUMBER: 36811 SUBJECT: The first three GRBs detected by SVOM: X-ray Upper Limits from EP-WXT DATE: 24/07/03 15:23:07 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

C. Y. Dai (NJU), J. Q. Peng, Q. C. Shui (IHEP, CAS), Y. L. Wang, C. C. Jin, Z. X. Ling, W. Yuan, Y. Liu, C. Zhang, H. Q. Cheng, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, X. Pan, H. Sun, W. X. Wang, Y. L. Wang, S. X. Wen, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang, D. H. Zhao (NAOC, CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team

We report on the X-ray upper limits from the observations of the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, for the first three GRBs detected by SVOM (Xiong et al. GCN #36805), GRB 240627B, GRB 240629A and GRB 240702A.

Among the three GRBs, the position of GRB 240702A has not been covered by the field-of-view of WXT after its detection by SVOM. Both GRB 240627B and GRB 240629A were serendipitously covered by the field-of-view of WXT multiple times after their detections by SVOM, but no new X-ray sources were found within 3 degrees of their positions.

The flux upper limits at the 5-sigma confidence level for GRB 240627B and GRB 240629A are detailed as follows.

Source | R.A | Dec. ｜ Obs. start time | Exposure (s) | Upper limit (erg/s/cm2) ------------------------------------------------------------------------------------------------------ GRB 240627B | 215.25 | 48.52 | 2024-06-27T20:21:43.000 | 586 | 4.43e-11 GRB 240627B | 215.25 | 48.52 | 2024-06-27T23:23:27.000 | 1233 | 2.90e-11 GRB 240629A | 314.4 | -35.7 | 2024-06-30T00:11:05.000 | 6429 | 1.18e-11 GRB 240629A | 314.4 | -35.7 | 2024-06-30T04:59:38.000 | 54140 | 3.93e-12 ------------------------------------------------------------------------------------------------------

The above observations were made with the WXT instrument during the commissioning phase of EP. 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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