TITLE: GCN CIRCULAR NUMBER: 44477 SUBJECT: GRB 260504B: SVOM/VT optical upper limits DATE: 26/05/05 15:53:02 GMT FROM: Huali Li at at NAOC, SVOM <lhl@nao.cas.cn> H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, 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), Y. Wang (PMO,CAS; UCB) report on behalf of the SVOM/VT team. SVOM/VT performed observations with an automatic slew to GRB 260504B detected by SVOM/ECLAIRs (sb26050402, Saccardi et al., GCN 44454), SVOM/GRM (Wang et al., GCN 44470), GECAM-B (Wang et al., GCN 44473) and Konus-Wind (Frederiks et al., GCN 44474). The observation started at 2026-05-04T09:34:59 UTC, 220 seconds post trigger and lasted for 6 orbits (about 8 hours), in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44454) or SVOM/MXT (Maggi et al., GCN 44468), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction: Mid time | Band | Exposure Time | 5-sigma upper limit 670 s VT_B 18*50 s > 22.5 mag 670 s VT_R 18*50 s > 22.5 mag 2.59 h VT_B 34*100 s > 23.0 mag 2.59 h VT_R 33*100 s > 23.0 mag Our result is consistent with the results from the rapid decay in SVOM/MXT (Saccardi et al., GCN 44454), upper limit of EP-FXT (Zhou et al., GCN 44467), optical non-detections by MASTER-OAFA(Podesta et al., GCN 44455), LCO (Turpin et al., GCN 44456), AST3-2 (Sun et al., GCN 44457) and REM (Brivio et al., GCN 44460). 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/44477. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...