TITLE: GCN CIRCULAR NUMBER: 39917 SUBJECT: GRB 250329A: SVOM/VT optical counterpart confirmation DATE: 25/03/29 08:01:15 GMT FROM: SVOM_group svomgroup@bao.ac.cn
B.-T. Wang (YNAO, CAS), Y.H. Cheng (SWIFAR, YNU), W.J. Xie, L.P. Xin, Y. L. Qiu, H. L. Li, C. Wu (NAOC), J. T. Palmerio(CEA/Irfu), Z. H. Yao, Y. Xu, P. P. Zhang, J. Wang, X. H. Han, Y. J. Xiao, H. B. Cai, J. Y. Wei (NAOC) report on behalf of the SVOM team:
SVOM performed an automatic slew on the burst triggered by SVOM/ECLAIRs (Wang et al., GCN 39916). SVOM/VT began observing the field automatically with the slew of the platform triggered on-board, in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With VHF downlinked data, an uncatalogued source was found in VT_R channel, and fading for about 0.4 mag in the third and fourth sequences.
The coordinates are R.A (J2000) =13:09:47.23 (197.44674 deg) DEC.(J2000) = +09:29:43.2 (+9.49532 deg) Error=0.5 arcseconds. The coordinates are consistent with the candidate reported (Watson et al., GCN 39915).
The magnitude is VT_R=20.1+/- 0.04 mag(AB) and VT_B>22.0 mag(AB,3sigma) with the mid time of 1.25 hours after the burst. We propose it is possible a medium/high redshift GRB, given on red coulor (Wang et al., 2020).
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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