TITLE: GCN CIRCULAR NUMBER: 39661 SUBJECT: GRB 250309B: SVOM/VT optical observation DATE: 25/03/11 06:47:44 GMT FROM: SVOM_group svomgroup@bao.ac.cn
Z. M. Wang, A. Li (BNU), Y. F. Liang (PMO), L. P. Xin, Y. L. Qiu, H. L. Li, Z. H. Yao, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM team:
The SVOM/VT conducted a ToO follow-up observation of ZTF25aaitvjt / AT2025dws (Stein et al., GCN 39639) which is considered as the optical candidate of Fermi GRB 250309B (Preis & Greiner, GCN 39629; McDermott et al., GCN 39635; McDermott et al., GCN circ. 39642) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously,
The optical candidate ZTF25aaitvjt / AT2025dws (Stein et al., GCN 39639; Pérez-Fournon et al., GCN 39643; Stein and Ahumada, GCN 39644; Moskvitin et al., GCN 39645; Perley et al., GCN 39646; Malesani et al., GCN 39647; Ducoin et al., GCN 39650; Shin et al, GCN 39654) is clearly detected in images.
The brightness in AB manigutude was estimated to be 20.20+/0.04 mag in VT_R, and 20.72+/-0.05 mag in VT_B stacked images, with an exposure time of 46*60 seconds, at the mid time of 0.974 days post 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.
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