TITLE: GCN CIRCULAR NUMBER: 41369 SUBJECT: GRB 250813B: SVOM/VT optical observations DATE: 25/08/14 12:16:34 GMT FROM: Liping Xin at NAOC, SVOM <xlp@nao.cas.cn> L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Y. N. Ma, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), B. T. Wang (YNAO) report on behalf of the SVOM/VT team. SVOM performed an automatic slew on the burst GRB 250813B triggered by SVOM/ECLAIRs (Xie et al., GCN 41354). SVOM/VT start the observations at 278 seconds after the burst, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The optical counterpart (Jelinek et al., GCN 41353 & GCN 41355; Schneider et al., GCN 41363; de Ugarte Postigo et al., GCN 41356) at the position consistent with the locations of Swift/XRT (Page et al., GCN 41359), EP/FXT (Wu et al., GCN 41361) and SVOM/MXT(Xie et al., GCN 41354, Gotz et al., GCN 41368), was clearly detected in both VT_R and VT_B. During the X-band data available, the brightness was fading from VT_R=16.61+/0.02 mag and VT_B=17.73+/-0.03 mag at 303 seconds post the burst to VT_R=20.9+/-0.1 mag and VT_B=22.1+/-0.2 mag at 4.27 hours after the burst. Our photometry was not corrected for Galactic extinction. 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. The SVOM point of contact for this burst is Wenjin Xie (xiewj@bao.ac.cn). Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/41369. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...