{
  "createdOn": 1777996382831,
  "subject": "GRB 260504B: SVOM/VT optical upper limits",
  "submittedHow": "web",
  "submitter": "Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>",
  "eventId": "GRB 260504B",
  "circularId": 44477,
  "body": "H. L. Li, L. P. Xin, C. Wu, Y. L. Qiu, Y. N. Ma, Z. H. Yao, J. R. Xu,  X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), Y. Wang (PMO,CAS; UCB) report on behalf of the SVOM/VT team.\n\nSVOM/VT performed  observations with an automatic slew to GRB 260504B detected by SVOM/ECLAIRs (sb26050402, Saccardi et al., GCN 44454), SVOM/GRM (Wang et al., GCN 44470), GECAM-B (Wang et al., GCN 44473) and Konus-Wind (Frederiks et al., GCN 44474). The observation started at 2026-05-04T09:34:59 UTC, 220 seconds post trigger and lasted for 6 orbits (about 8 hours), in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously. \n\nNo uncatalogued sources were detected within the error box of SVOM/ECLAIRs (Saccardi et al., GCN 44454) or SVOM/MXT (Maggi et al., GCN 44468), compared to the Legacy Survey. The following measurements are in the AB magnitude and are not corrected for Galactic extinction:\n\nMid time |  Band   | Exposure Time | 5-sigma upper limit\n 670 s      VT_B       18*50 s        > 22.5 mag    \n 670 s      VT_R       18*50 s        > 22.5 mag\n2.59 h      VT_B      34*100 s        > 23.0 mag    \n2.59 h      VT_R      33*100 s        > 23.0 mag\n\nOur result is consistent with the results from the rapid decay in SVOM/MXT (Saccardi et al., GCN 44454), upper limit of EP-FXT (Zhou et al., GCN 44467), optical non-detections by MASTER-OAFA(Podesta et al., GCN 44455), LCO (Turpin et al., GCN 44456), AST3-2 (Sun et al., GCN 44457) and REM (Brivio et al., GCN 44460).\n\nThe 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.",
  "format": "text/plain"
}