TITLE: GCN CIRCULAR NUMBER: 40992 SUBJECT: GRB 250706B: SVOM/VT optical observation DATE: 25/07/06 18:45:55 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> After the trigger by SVOM/ECLAIRs at 2025-07-06T17:06:04 UTC (T0), SVOM performed an automatic slew on the burst location (Palmerio et al., GCN 40989). SVOM/VT began observing the field at 2025-07-06T17:10:48, 283.83 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 50: This candidate was flagged as un uncatalogued source whose magnitude varied with 3 sigma significance. The position of this candidate is R.A., Dec. 41.2311, -50.0612 degrees, corresponding to: R.A. (J2000) = 2h44m55.5s Dec. (J2000) = -50d03m40.4s with an uncertainty of 1 arcsec. This location is within the R90 uncertainty region of the SVOM/MXT onboard localization. This location is consistent with the optical afterglow reported by Zhu et al. (GCN 40991). The source was detected in both VT_R and VT_B, and was fading between the first 2 VT observing sequences. The candidate's magnitudes are: | date-obs (UTC)  | mid-time  | exposure  | band  | mag(AB)  | | -------------------- | ----------- | --------- | ----- | ------------- | | 2025-07-06T17:10:48  | 7.23 min  | 6*50 sec  | VT_B  | 14.90 ± 0.01  | | 2025-07-06T17:10:48  | 7.23 min  | 6*50 sec  | VT_R  | 14.48 ± 0.01  | | 2025-07-06T17:15:48  | 12.23 min  | 6*50 sec  | VT_B  | 15.17 ± 0.01  | | 2025-07-06T17:15:48  | 12.23 min  | 6*50 sec  | VT_R  | 14.65 ± 0.01  | Magnitudes were not corrected for dust extinction. Given the VT colour of the counterpart, it might be a low redshift gamma-ray burst. 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. The SVOM/VT point of contact for this burst is Jesse Palmerio: palmerio@cea.fr. View this GCN Circular online at https://gcn.nasa.gov/circulars/40992. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...