TITLE: GCN CIRCULAR NUMBER: 39817 SUBJECT: EP250321a: SVOM/VT optical observation DATE: 25/03/21 15:58:18 GMT FROM: Xuhui Han at NAOC/SVOM hxh@nao.cas.cn
X. H. Han, Z. H. Yao, L. P. Xin, Y. L. Qiu, H. L. Li, Y. Xu, P. P. Zhang, W. J. Xie, J. Wang, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC) report on behalf of the SVOM mission team.
SVOM/VT conducted ToO follow-up observations of the X-ray transient EP250321a (Hu et al., GCN 39800) at the location of WXT position in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.
The optical counterpart of EP250321a (Trigger ID: 01709133009, Fu et al., GCN 39804; Perez-Garcia et al., GCN 39805; Brivio et al., GCN 39807; Zhu et al., GCN 39809; Becerra et al., GCN 39810; Pérez-Fournon et al., GCN 39812; Lee et al., GCN 39815) was clearly detected in VT_R and VT_B images.
The brightness in AB magnitude was estimated to be:
Mid time UTC | Band | Exposure Time (second) | Magnitude | Magnitude error 2025-03-21T10:29:29 | VT_B | 2940 | 21.85 | 0.09 2025-03-21T10:29:29 | VT_R | 2940 | 19.39 | 0.03
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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