TITLE: GCN CIRCULAR NUMBER: 41976 SUBJECT: GRB 250924A: SVOM/VT optical observation DATE: 25/09/25 03:51:53 GMT FROM: SVOM_group svomgroup@bao.ac.cn
Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), R. Z. Li (YNAO), D. F. Kong (GXU), report on behalf of the SVOM/VT team:
SVOM/VT performed a Target of Opportunity observation of GRB 250924A detected by Swift (Siegel et al., GCN 41959; Osborne et al., GCN 41973; Campana et al., GCN 41974; Siegel et al., GCN 41975). SVOM/VT began observing the field at 2025-09-24T11:07:35 UTC, 2.818 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart is detected in both VT_B and VT_R, the magnitudes are as follows:
mid time (h) | exposure time (s) | band | mag (AB) | mag err -------------|-------------------|------|----------|-------- 3.103 | 38*50 | VT_B | 21.15 | 0.06 3.089 | 40*50 | VT_R | 20.25 | 0.05 Our photometry was not corrected for Galactic extinction.
The position and the brightness are consistent with the previous reports (Siegel et al., GCN 41959; Becerra et al., GCN 41960; Lipunov et al., GCN 41962; Schneider et al., GCN 41963; Freeberg et al., GCN 41968; Pankov et al., GCN 41969; Zheng et al., GCN 41970; Saikia et al., GCN 41971; Mo et al., GCN 41972; Siegel et al., GCN 41975).
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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.
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