TITLE: GCN CIRCULAR NUMBER: 41299 SUBJECT: GRB 250807A: SVOM/VT optical continued observation DATE: 25/08/09 09:00:02 GMT FROM: Yinuo Ma mayn@bao.ac.cn

Y. N. Ma, Z. H. Yao, L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA) report on behalf of the SVOM/VT team.

SVOM/VT conducted continued observations of GRB 250807A detected by Swift/BAT（Klingler et al., GCN 41262), AstroSat-CZTI (Salunke et al., GCN 41281), SVOM/GRM (Wang et al,. GCN 41283) and Konus-Wind (Svinkin et al,. GCN 41295).

The magnitude of the optical afterglow (Klingler et al., GCN 41262; Ma et al., GCN 41274; Shilling et al., GCN 41291) is: mid time | exposure time (s) | band | mag (AB) | mag err -----------|-------------------|------|----------|-------- 18.25h | 31*70 | VT_R | 21.59 | 0.08

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 Centre 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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