TITLE: GCN CIRCULAR NUMBER: 39931 SUBJECT: GRB 250329B: SVOM/VT optical upper limit DATE: 25/03/29 19:13:49 GMT FROM: Liping Xin at NAOC, SVOM <xlp@nao.cas.cn> L.P. Xin, H.L. Li, Y. L. Qiu, C. Wu, Z.H. Yao, Y. Xu, P.P. Zhang, J. Wang, Y.N. Ma, X.H. Han, H.B. Cai, J.Y. Wei, W.J. Xie (NAOC), Y.H. Cheng (SWIFAR, YNU), B.T. Wang (YNAO, CAS), J. T. Palmerio (CEA) report on behalf of the SVOM/VT team: SVOM performed a Target of Opportunity observation of GRB 250329B (Xie et al., GCN 39925), starting at 2025-03-29T15:00:16 UT, ~2.85 hours after the SVOM/Eclairs trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. No any source was detected in the stacked images within the errorbox of the X-ray Swift/XRT [source #1]( https://www.swift.ac.uk/SVOM/SVOM_FIELD00008/) . The 3 sigma limits in VT_R is 23.1 mag (AB) at the middle time of 4.0 hours after the burst. This result is consistent with the reports (Xin et al., GCN 39926, Chen et al., GCN 39929). Deeper or redder follow-ups are encouraged to investigate the nature of the burst. 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/39931. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...