TITLE: GCN CIRCULAR NUMBER: 40678 SUBJECT: GRB 250610B: SVOM/VT optical counterpart DATE: 25/06/10 23:35:24 GMT FROM: Liping Xin at NAOC, SVOM xlp@nao.cas.cn
H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, Y. N. Ma, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), A. Saccardi, J. Rodriguez, N. Dagoneau (CEA), C. Van Hove (IJCLab) report on behalf of the SVOM mission team.
SVOM performed a Target of Opportunity observation of GRB 250610B detected by SVOM/Eclairs (Saccardi et al., GCN 40671). SVOM/VT began observing the field at 2025-06-10 17:04:26 UTC, 0.52 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
An uncatalogued source, compared to legacy survey, is found using VT X-band data, within the error box of Swift/XRT1 at R.A., Dec 200.179739, 31.10496 degrees:
RA (J2000) = 13:20:43.1 Dec (J2000) = +31:06:17.9
with an uncertainty of 0.5 arcsec.
The source is detected in both VT_R and VT_B, and was fading by 0.3 mag in 2 orbits, the magnitudes are:
Mid-time after the burst | exposure time (s) | band | mag (AB) | mag err --------------------|-------------------|------|----------|-------- 1.234 hour | 70 | VT_B | 20.7 ｜ 0.1 1.234 hour | 70 | VT_R | 20.3 ｜ 0.1
This position and the brightness is consistent with the reports (Schneider et al., GCN 40676, Gompertz et al., GCN 40677)
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Centre 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.
The Burst Advocate (BA) on shift for this alert is Andrea Saccardi@cea.fr.
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