TITLE: GCN CIRCULAR NUMBER: 42987 SUBJECT: GRB 251203C: SVOM/VT optical counterpart DATE: 25/12/04 14:05:47 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H.L. Li (NAOC), D. Turpin (CEA), Y.N. Ma, L.P. Xin, Y. L. Qiu, C. Wu, Z.H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), M. Brunet, N. A. Webb (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the field of GRB 251203C triggered by SVOM (Brunet et al., GCN 42976). The observation started at 2025-12-03T21:46:05 UTC, i.e., 3.2 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. An uncatalogued source was detected within the ECLAIRs's error box (Brunet et al., GCN 42976), compared to the Legacy survey catalog. The position is at R.A., Dec. = 51.701538, -7.382688 degrees, equivalent to: R.A. (J2000) = 03:26:48.36 Dec. (J2000) = -07:22:57.67 with an uncertainty of 0.5 arcsec. The measurements in AB magnitudes are given below: Mid_time Band Exposure Time Magnitude (AB) 3.3 hour VT_B 970 sec 22.1+/-0.1 mag 3.3 hour VT_R 970 sec 21.7+/-0.1 mag 9.7 hour VT_B 4430 sec 23.0+/-0.3 mag 9.7 hour VT_R 4430 sec 22.4+/-0.2 mag Our photometry was not corrected for Galactic extinction. As this source has significantly faded during our observations, we suggest it is the optical afterglow of GRB 251203C. 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/42987. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...