TITLE: GCN CIRCULAR NUMBER: 40246 SUBJECT: GRB 250424A: SVOM/VT optical observation DATE: 25/04/25 11:38:33 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> Z.H. Yao(NAOC), X. H. Han(NAOC), Y. D. Hu(GXU),L. Zhang(IHEP), X. L. Chen(YNU), L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, L. Lan, J. Y. Wei (NAOC) report on behalf of the SVOM mission team. SVOM/VT conducted ToO follow-up observations of the GRB 250424A(Francile et al., GCN 40222). The observation started on 2025 Apr 24 09:26:29 UT in VT_B(400nm-650nm) and VT_R (650nm-1000nm)channel simultaneously. The candidate(Francile et al., GCN 40222; Cenko et al., GCN 40224; Brivio et al., GCN 40225; Becerra et al., GCN 40226; Saccardi et al., GCN 40228; de Wet et al., GCN 40229; Ducoin et al., GCN 40230; D. Turpin et al., GCN 40240; Dutton et al., GCN 40241; and Siegel et al., GCN 40244) was clearly detected in stacked images of both channels. The brightness in AB magnitude was estimated to be: Mid time (hour) | Band | Exposure Time (second) | Magnitude | Magnitude error 2.98 | VT_B | 60x50 | 19.89 | 0.03 2.98 | VT_R | 60x50 | 18.96 | 0.02 The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/40246. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...