TITLE: GCN CIRCULAR NUMBER: 43623 SUBJECT: GRB 260204A: SVOM/VT confirms fading of the optical afterglow DATE: 26/02/06 04:13:44 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L.P. Xin, 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/Irfu), R. Z. Li (YNAO), C. W. Wang (IHEP) report on behalf of the SVOM/VT team. SVOM/VT performed ToO observation to the GRB 260204A triggered by SVOM/ECLAIRs (sb26020403, Pillas et al., GCN 43613), which was also detected by Fermi (Fermi GBM team, GCN 43618) and followed by Swift (Evan et al., GCN 43622), LCO (Turpin et al., GCN 43616; Malesani et al. GCN 43621), GOTO (Kumar et al, GCN 43617) and MASTER (Lipunov et al., GCN 43619). The observation started at 2026-02-05T07:04:40 UTC, i.e., 16.27 hour post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. By stacking images of 47*50 sec in VT_R and 44*50 sec in VT_B, the counterpart (Li et al., GCN 43620; Malesani et al. GCN 43621) was confirmed to be fading with the brightness of VT_R~23.1+/-0.3 mag and VT_B>23.3 mag at the mid time of 18.0 hours post trigger. Combined with the earlier detection (Li et al., GCN 43620), the optical decay slope was -0.90. Our photometry was in AB magnitude and not corrected for Galactic extinction. 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/43623. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...