TITLE: GCN CIRCULAR NUMBER: 40830 SUBJECT: GRB 250625A: SVOM/VT optical confirmation DATE: 25/06/26 00:20:46 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, 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), A. Li (BNU) report on behalf of the SVOM/VT team
SVOM/VT performed a Target of Opportunity observation of GRB 250625A detected by Swift-BAT（Ferro et al., GCN 40825) and Fermi-GBM (GCN #40824). The observation began at 2025-06-25T16:50:36 UTC, 45.7 minutes after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The optical counterpart (Moskvitin et al., GCN 40828) within the errorbox of Swift/XRT (Beardmore et al., GCN 40827) was detected in the 38*70 sec stack image with a magnitude of VT_B=22.5+/-0.15 mag in AB magnitude with a mid time of 69 min after the burst.
The counterpart is also detected in VT_R band in the stack image, but it has some contaimination from the blooming light from the nearby bright source. More detailed data analysis is on going.
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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