TITLE: GCN CIRCULAR NUMBER: 44080 SUBJECT: GRB 260321A: SVOM/VT optical upper limits DATE: 26/03/22 14:10:30 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), M. Brunet (IRAP), O. Godet (IRAP) report on behalf of the SVOM/VT team. SVOM/VT performed an observation with automatic slew to the field of GRB 260321A triggered by SVOM/ECLAIRs (sb26032123, Brunet et al., GCN 44071). The observation started at 2026-03-21T18:57:18 UTC, i.e., about 45 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. No credible sources were detected within the error box of ECLAIRs (Brunet et al., GCN 44071), compared to the Legacy survey catalog. The 5 sigma upper limits in AB magnitude are derived as follows: Mid time | Band | Exposure Time | 5 sigma upper limit 1.13 hour VT_B 53*50 sec > 22.7 mag 1.12 hour VT_R 42*50 sec > 22.5 mag More detailed analysis is still ongoing. 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/44080. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...