TITLE: GCN CIRCULAR NUMBER: 38838 SUBJECT: GRB 250106A: SVOM/VT 2nd optical deep observation DATE: 25/01/07 09:31:41 GMT FROM: SVOM_group svomgroup@bao.ac.cn

SVOM/VT commissioning team: Y. L. Qiu, H. L. Li, C. Wu, D. H. Zhao, L. P. Xin, X. H. Han, J. Wang, W. J. Xie, H. B. Cai, Y. Xu, Y. J. Xiao, P. P. Zhang, J. S. Deng, L. Lan, X. M. Lu, R. S. Zhang, Z. H. Yao (NAOC), J. Zhang, L. J. Dan, G. Y. Zou, C. J. Wang, Y. F. Du, C. Huang (XIOPM)

SVOM JSWG: Jian-Yan Wei (NAOC), Bertrand Cordier (CEA), Shuang-Nan Zhang (IHEP), Stéphane Basa (LAM), Arnaud Claret (CEA), Zi-Gao Dai (USTC), Frédéric Daigne (IAP), Jin-Song Deng (NAOC), Olivier Godet (IRAP), Andrea Goldwurm (APC), Diego Götz (CEA), Xu-Hui Han (NAOC), Cyril Lachaud (APC), En-Wei Liang (GXU), Yu-Lei Qiu (NAOC), Susanna Vergani (Obs.Paris), Jing Wang (NAOC), Chao Wu (NAOC), Li-Ping Xin (NAOC), Shao-Lin Xiong (IHEP), Bing Zhang (UNLV)

report on behalf of the SVOM team:

The SVOM/VT conducted TOO observations of GRB 250106A (Zhao et al., GCN 38826) at 8.88 hr after the trigger. The observations were carried out in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously.

The candidate reported by Qiu et al. (GCN 38829) were detected in both of stacked images of VT_B and VT_R. The brightness are, channel (t-T0)_mid(hr) exptime mag(AB) VT_B 13.25 149x100s 23.5 +/-0.2 VT_R 13.26 142x100s 22.4 +/-0.1

No definite fading was found compared to brightness reported (Qiu et al., GCN 38829). This observation is consistent with the result (Izzo et al. GCN 38834). Thus, this source is not a good candidate for the burst.

A new source with a low S/N with a magnitude of VT_R~24.0 mag was tentatively detected near the errorbox of XRT source #1 (Osborne et al. GCN 38830), with a distance of 4.0 arcseconds from the XRT source #1. Its position is RA=117.2372, DEC=63.8132 deg, which is equivalent to: RA (J2000) : 07:48:56.93 Dec (J2000): +63:48:47.5 with an uncertainty of 0.5 arcsec.

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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