TITLE: GCN CIRCULAR NUMBER: 38729 SUBJECT: GRB 241229B: SVOM/VT optical candidate DATE: 24/12/30 16:15:59 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> SVOM/VT commissioning team: Y. L. Qiu, H. L. Li (NAOC), A. Li (BNU), Y. F. Liang (PMOC), L. P. Xin, C. Wu, 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 a ToO follow-up observations of the Fermi (GCN 38698) and Swift triggered GRB 241229B (GCN 38699) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously, from 12.09 hours to 15.5 hours after the burst. A new optical source was detected within the errorbox of XRT (GCN 38708) in VT_R stacked image, compared to the PanSTARRS catalog. The brightness of the source was estimated to be 21.8 ± 0.1 mag in AB magnitude in VT_R image at the mid time of 13.8 hours post the burst, with a total exposure time of 34*60 seconds. The source was not detected in VT_B stacked image with 3 sigma upper limit of ~23.2 mag in AB magnitude. The source is located at RA, Dec = 274.1803, 74.6851 deg, which is equivalent to: RA (J2000) : 18:16:43.271 Dec (J2000): +74:41:06.04 with an uncertainty of 0.5 arcsec. We do not confirm the fading of the source, but which might be the candidate for the gamma-ray burst. More deep follow-ups are encouraged for the nature of the source. 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/38729. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...