TITLE: GCN CIRCULAR NUMBER: 44799 SUBJECT: GRB 260603A: SVOM/VT optical observations DATE: 26/06/03 12:00:59 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, J. R. Xu, L. P. Xin, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), R. Z. Li (YNAO) and Z. M. Wang (BNU) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observations to the field of GRB 260603A triggered by SVOM/ECLAIRs (sb26060303, Zhao et al., GCN 44787). The observation started at 2026-06-03T07:04:07 UTC, 1.44 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The optical counterpart (Guelfand et al., GCN 44791; GCN 44797) was detected by VT in both channels. The following measurements are in the AB magnitude without correction for Galactic extinction: Mid time | Band | Exposure Time | Brightness 1.78 h VT_B 36*70 s 22.08 +/- 0.12 mag 1.78 h VT_R 30*70 s 21.37 +/- 0.10 mag 3.41 h VT_B 36*70 s 22.40 +/- 0.14 mag 3.40 h VT_R 31*70 s 21.74 +/- 0.11 mag The source showed a fading slope of about -0.53 during the observations above. 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/44799. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...