TITLE: GCN CIRCULAR NUMBER: 42136 SUBJECT: GRB 251005C: SVOM/VT optical fading DATE: 25/10/07 03:27:51 GMT FROM: Huali Li at at NAOC, SVOM lhl@nao.cas.cn
H. L. Li, L. P. Xin, 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) report on behalf of the SVOM/VT team.
A second ToO observation from SVOM/VT was performed to the field of GRB 251005C (Page et al., GCN 42113; Smith et al., GCN 42118; Arya et al., GCN 42122; Luo et al., GCN 42135) which stared at 2025-10-06T17:36:01 UTC, I.e., 25.5 hours post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical candidate (Palmerio et al. , GCN 42123; Yadav et al., GCN 42127; Watson et al., GCN 42129) was detected in VT_R stacked image at the mid time of 27.4 hours post trigger with the brightness of VT_R~23.3+/-0.2 mag. Combining earlier magnitudes from VT, the source was fading with a power-law temporal slope of about -0.7.
Our photometry was derived in AB magnitude and 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.
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