TITLE: GCN CIRCULAR NUMBER: 42819 SUBJECT: LIGO/Virgo/KAGRA S251105aj: SVOM/VT optical observations and preliminary results on SVOM J2320.0-2901 DATE: 25/11/24 15:06:20 GMT FROM: Yinuo Ma <mayn@bao.ac.cn> Y. N. Ma, H. L. Li, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, 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), H. Yang, O. Godet, J.-L. Atteia, M. Brunet, S. Guillot (IRAP), M. Pillas (IAP) report on behalf of the SVOM/VT team. SVOM/VT performed a Target of Opportunity observation of the high-energy transient SVOM J2320.0-2901 detected by SVOM/ECLAIRs (Yang et al., GCN 42797), right after S251105aj reported by LIGO/Virgo/KAGRA (The LIGO-Virgo-Kagra Collaboration, GCN 42587; GCN 42616). The observation began at 2025-11-16T00:47:45 UT, 10.5 days after SVOM/ECLAIRs detection, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The VT field of view covered 96% of the 90% C.L. ECLAIRs error region, but no uncataloged sources were detected within the error box of ECL. VT also covered three EP/FXT sources (source#1: RA, Dec = 349.8643, -29.0602 deg; source#2: 350.1419, -29.0148 deg; source#3: 349.9737, -28.8522 deg) reported by Guillot et al. (GCN 42818). None of the known sources became apparent brighter within errorbox of three FXT candidates compared with Legacy Survey DR10. The 3 sigma upper limit was VT_R > 23.6 mag and VT_B > 23.8 mag with the exposure time of 65*70 sec. Further analysis is ongoing. 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/42819. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...