TITLE:   GCN CIRCULAR
NUMBER:  44921
SUBJECT: GRB 260610B / AT2026owq: SVOM/VT optical observations
DATE:    26/06/12 08:27:15 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, J. R. Xu, 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) and J. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.

SVOM/VT performed a ToO observation of GOTO26fua/AT2026owq (O'Neil et al., GCN 44903; Watson et al., GCN 44905; Zhu et al.,  GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920), a possible counterpart of GRB 260610B (Fermi GBM Team, GCN 44901). The observation started at 2026-06-11T13:05:40 UTC, i.e., 13.32 hours post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.

The OT was clearly detected in both channels. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time | Brightness
14.50 h    VT_B    30*70 s       20.10 +/-0.06 mag
16.12 h    VT_B    29*70 s       20.16 +/-0.06 mag
14.52 h    VT_R    28*70 s       19.38 +/-0.06 mag
16.15 h    VT_R    26*70 s       19.49 +/-0.06 mag

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.