TITLE: GCN CIRCULAR NUMBER: 40351 SUBJECT: GRB 250504A: SVOM/VT upper limit DATE: 25/05/05 14:53:47 GMT FROM: SVOM_group svomgroup@bao.ac.cn
L. P. Xin, Y. L. Qiu, H. L. Li, C. Wu, Z. H. Yao, Y. N. Ma, D.H. Zhao, 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) report on behalf of the SVOM/VT Instrument Center:
SVOM/VT conducted ToO follow-up observations of GRB 250504A detected by Fermi (Fermi/GBM team, GCN 40342; Bala et al., GCN 40346) and Swift (Moss et al., GCN 40343). The observation started on 2025-05-05T01:11:01 UT, 2025 May 05, ~1.75 hr after the burst.
Our preliminary analysis shows no detection of an optical counterpart in VT_B-band stacked images (3975 s total effective exposure) at both the de Wet et al. (GCN 40347) position and the enhanced XRT position (4.0 arcsec error radius; Osborne et al. GCN 40345), with a 3 sigma upper limit of VT_B > 22.0 mag (AB) at 2.74 hr post-burst.
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.
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