TITLE:   GCN CIRCULAR
NUMBER:  45851
SUBJECT: GRB 261007A / EP261007a: SVOM/VT optical observations
DATE:    26/10/08 07:33:35 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, Y. N. Ma, L. P. Xin, C. Wu, Y. L. Qiu, Z. H. Yao, J. R. Xu, 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/Irfu), W. L. Zhang (PMO), X. Tian (GXU) report on behalf of the SVOM/VT team.

SVOM/VT performed observations with automatic slew to the field of GRB 261007A triggered by SVOM/ECLAIRs (sb26100701, Goto et al., GCN 45824). This burst was also detected by SVOM/GRM (Goto et al., GCN 45824), Fermi-GBM (Malacaria et al., GCN 45830) and Einstein Probe as EP261007a (Wen et al., GCN 45828). The current available VT data started at 2026-10-07T13:00:15 UTC, approximately 7.317 hr post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. 

The optical counterpart (Zheng et al., GCN 45825; Mohan et al., GCN 45832; Saccardi et al., GCN 45837; Shi et al., GCN 45838; An et al., GCN 45840; Arya et al., GCN 45841; Rehemtulla et al., GCN 45843; Ruiz-Laguna et al., GCN 45844; Angulo et al., GCN 45848) with the redshift z=2.101 (Saccardi et al., GCN 45829) was clearly detected in both channels. 

The preliminary measurements are given in AB magnitudes and are not corrected for Galactic extinction:

Mid time | Band | Exposure Time |  Brightness
15.65 hr   VT_B      21*70 s     21.4+/-0.1 mag  
15.66 hr   VT_R      16*70 s     21.0+/-0.1 mag

The light curves show fading behavior in both channels with a slope of -1.4 for our available data spanning 7.6 hr to 15.7 hr.

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.