GCN Circular 40960
Subject
EP250704a / GRB 250704B: SVOM/VT optical blue counterpart
Event
Date
2025-07-04T21:08:26Z (14 days ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
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), J.X Cao (GXU), Y.H Cheng (SWIFAR, YNU) report on behalf of the SVOM/VT team.
SVOM/VT performed a Target of Opportunity observation of GRB 250704B（Wang et al., GCN 40940) and EP250704a (Li et al., GCN 40941) . The observation began at 2025-07-04T12:58:50 UTC , 4.68 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
The afterglow (Schneider et al. GCN 40942, Malesani et al., GCN 40945, Gillanders et al., GCN 40958) within the errorbox of Swift/XRT (Evens et al., GCN 40951) and EP/FXT (Li et al., GCN 40956) was detected in both VT_B and VT_R images.
The brightness was about 20.4 mag in AB magnitude in both bands with a VT color of roughly zero, indicating a blue optical source.
Our photometry was not corrected for Galactic extinction.
More follow-ups are encouraged.
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.