TITLE: GCN CIRCULAR NUMBER: 44568 SUBJECT: GRB 260511B: SVOM/VT optical observations DATE: 26/05/12 04:28:34 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, C. Wu, Y. L. Qiu, L. P. Xin, Y. N. Ma, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), L. Zhang (IHEP) and D. Kong (GXU) report on behalf of the SVOM/VT team. SVOM/VT performed observations of GRB260511B triggered by SVOM/ECLAIRs (sb26051102, Godet et al., GCN 44543). The burst was also detected by Fermi-GBM (Fermi GBM team, GCN 44542; Roberts et al., GCN 44554)，AstroSat (Arya et al., GCN 44560) and NuSTAR (Waratkar et al. GCN 44556). Our available data via automatic slew started at 2026-05-11T14:26:43 UTC, approximately 3.45 hours post trigger, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. The ToO observations started at 2026-05-11T20:37:09 UTC, about 9.62 hours post trigger. The afterglow (Wu et al. GCN 44547; Sasada et al. GCN 44549; Jiang et al. GCN 44551; Wu et al. GCN 44552; Li et al. GCN 44557; Vijaykumar et al. GCN 44561) with the redshift of z=2.006 (Postigo et al., GCN 44565) was clearly detected in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | Brightness 3.450 h VT_B 100 s 18.00 +/- 0.03 mag 3.450 h VT_R 100 s 17.61 +/- 0.03 mag 10.159 h VT_B 100 s 19.52 +/- 0.05 mag 10.159 h VT_R 100 s 19.05 +/- 0.05 mag The source showed a fading slope of about -1.3 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/44568. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...