{
  "eventId": "GRB 251013C",
  "subject": "GRB 251013C: SVOM/VT optical observation",
  "body": "J. T. Palmerio (CEA/Irfu), Ny Avo Rakotondrainibe, C. Adami (LAM), H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu (NAOC) report on behalf of the SVOM/VT team:\n\nAfter the trigger by SVOM/ECLAIRs at 2025-10-13T17:39:42 UTC (T0), SVOM performed an automatic slew on the burst location (Rakotondrainibe et al., GCN 42222). SVOM/VT began observing the field at 2025-10-13T17:44:04, 261.08 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.\n\nFrom 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.\n\nVT_ID 117:\n  This bright candidate was flagged as a catalogued source but significantly brighter than its catalogued magnitude.\n  The position of this candidate is R.A., Dec. 345.8356, -0.2103 degrees, corresponding to:\n  R.A. (J2000) = 23h03m20.6s\n  Dec. (J2000) = -0d12m37.1s\n  with an uncertainty of 0.5 arcsec.\n  \n  This location is within the R90 uncertainty region of the SVOM/MXT onboard localization.\n  The source was detected in both VT_R and VT_B. The candidate's magnitudes are:\n  \n  | date-obs (UTC)       | mid-time    | exposure  | band  | mag(AB)       |\n  | -------------------- | ----------- | --------- | ----- | ------------- |\n  | 2025-10-13T17:44:04  | 6.85 min    | 6*50 sec  | VT_B  | 15.38 ± 0.01  |\n  | 2025-10-13T17:44:04  | 6.85 min    | 6*50 sec  | VT_R  | 14.76 ± 0.01  |\n\n  Magnitudes were not corrected for dust extinction.\n  The VT color of the counterpart suggests it is not very high redshift or highly extinguished.\n\nThe 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.\nSVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.",
  "createdOn": 1760379516906,
  "submittedHow": "web",
  "circularId": 42223,
  "submitter": "SVOM_group <svomgroup@bao.ac.cn>",
  "bibcode": "2025GCN.42223....1P",
  "format": "text/plain"
}