TITLE: GCN CIRCULAR NUMBER: 43189 SUBJECT: GRB 251222A: SVOM/VT optical candidate DATE: 25/12/22 17:48:55 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> J. T. Palmerio (CEA/Irfu), Y. L. Qiu, C. Wu, L. P. Xin (NAOC) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs at 2025-12-22T17:05:46 UTC (T0), SVOM performed an automatic slew on the burst location (Yang et al., GCN 43188). SVOM/VT began observing the field at 2025-12-22T17:10:47, 300.27 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below. VT_ID 117: This bright candidate was flagged as an uncatalogued fading source. The position of this candidate is R.A., Dec. 77.1948558, -7.2135525 degrees, corresponding to: R.A. (J2000) = 05h08m46.8s Dec. (J2000) = -07d12m48.8s with an uncertainty of 0.5 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. The source was detected in both VT_R and VT_B. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | band | mag(AB) | | -------------------- | ----------- | --------- | ----- | ------------- | | 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_B | 18.70 ± 0.01 | | 2025-10-13T17:44:04 | 7.5 min | 6*50 sec | VT_R | 17.89 ± 0.01 | Magnitudes were not corrected for dust extinction. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/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/43189. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...