{
  "circularId": 40089,
  "body": "L. J. Chen(GXU), L. P. Xin(NAOC), Y. G. Yang(HNU), X. H. Han, C. WU, Y. L. Qiu, J. Wang, H. L. Li, X .M. Lu, R. S. Zhang, Y. Xu, L. Huang, H. B. Cai, Y. J. Xiao, P. P. Zhang, L. Lan,  W. J. Xie, Z. H. Yao, J. Y. Wei(NAOC), X. G. Wang, E. W. Liang(GXU) report on behalf of the SVOM follow-up team:\n\n\nWe observed the field of EP250404a detected by Einstein Probe (Hu et al., GCN 40051), which is temporally and spatially consistent with GRB 250404A (Fermi team, GCN 40050), with the GWAC-F50A and GWAC-F60 at Xinglong Observatory, China. F50 started observing at 2025-04-04T14:25:34 UTC and lasted until 2025-04-04T15:36:36 with 9 frames in R-band and 15 frames in I-band. F60A started observing at 2025-04-04T14:24:56 UTC and lasted until 2025-04-04T15:24:21 with 25 frames in R-band. F60B started observing at 2025-04-04T14:25:05 UTC and lasted until 2025-04-04T15:24:28 with 25 frames in R-band.\n\nThe optical counterpart of GRB 250404A / EP250404a (Jiang et al., GCN 40052; Perez-Garcia et al., GCN 40053; Du et al., GCN 40058; Zhu et al., GCN 40061; Konno et al., GCN 40063; Odeh et al., GCN 40064; He et al., GCN 40069; Pérez-Fournon et al., GCN 40071; Jelinek et al., GCN 40072; Rakotondrainibe et al., GCN 40073; Taguchi et al., GCN 40074; Brivio et al., GCN 40075; Ruocco et al., GCN 40076; Martin-Carrillo et al., GCN 40080; Pavoni et al., GCN 40083; Li et al., GCN 40084; Pankov et al., GCN 40086), was clearly detected in our images.\n\nThe afterglow shows a first brightening and then a single decay with a peak magnitude of R~14.3 mag, calibrated to the USNO B1.0 catalog, at about 1000 sec after the burst.\n\nTwo 60cm GWAC-F60(A/B) are operated by Guangxi University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 19*19 arcmin.  The 50cm telescope (F50A) is operated by Huaibei Normal University and NAOC, CAS, at Xinglong Observatory, China. The field of view is 27*27 arcmin.",
  "submitter": "Chen Liang-Jun at Guangxi University <chenlj@st.gxu.edu.cn>",
  "createdOn": 1743942440915,
  "format": "text/plain",
  "subject": "GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations",
  "bibcode": "2025GCN.40089....1C",
  "submittedHow": "web",
  "eventId": "GRB 250404A"
}