TITLE: GCN CIRCULAR NUMBER: 40875 SUBJECT: GRB 250628B: SVOM/VT optical upper limit DATE: 25/06/30 09:34:49 GMT FROM: Huali Li at at NAOC, SVOM lhl@nao.cas.cn
H. L. Li, Y. L. Qiu, L. P. Xin, C. Wu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Z. H. Yao, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), D. Dornic (CPPM)，J-G. Ducoin（CPPM）report on behalf of the SVOM/VT team. SVOM/VT performed ToO follow-up observations on the GRB 250628B (SVOM burst-id sb25062804, Dornic et al., GCN 40862) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation started on 2025-06-28T20:33:10 UT, ie. 4.06 hours after the SVOM T0 time.
No uncatalogued sources are detected in single or stacked images at the position of the Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00021/) and EP (Zhang et al., GCN 40874), compared to the Legacy survey. The 3 sigma upper limit magnitudes are derived as below:
Mid_time | Band | Exposure Time | Upper limit (AB) 5.8 hour VT_B 50*70 sec 23.6 mag 5.8 hour VT_R 49*70 sec 23.4 mag
Also no apparent variation is found for the catalogued sources that lie within the errorbox of the Swift/XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00021/) and EP (Zhang et al., GCN 40874). 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.
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