TITLE:   GCN CIRCULAR
NUMBER:  42163
SUBJECT: GRB 251007B: SVOM/VT optical candidate
DATE:    25/10/08 08:36:55 GMT
FROM:    Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>

H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, 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), J. Palmerio (CEA), N. A. Webb, O. Godet  report on behalf of the SVOM/VT Instrument Center: 

SVOM/VT conducted ToO follow-up observations of GRB 251007B (sb25100703) (Melandri et al., GCN 42147; Webb et al., GCN 42148). The observation started on 2025-10-07T21:41:47 UT, 1.98 hours after the burst, in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.

Within the error box of enhanced XRT position (Osborne et al., GCN 42159), an uncatalogued source was detected in both channels of VT, compared to the PanSTARRS catalogue. The position is at R.A., Dec. = 102.1329813, -10.3040289 degrees, equivalent to:
R.A. (J2000) =  6:48:31.92
Dec. (J2000) =  -10:18:14.50
with an uncertainty of 0.5 arcsec.

The magnitudes are as follows:

Mid_time     |  Band   | Exposure Time  |  Magnitude (AB)
4.82 hour       VT_R       43*70 sec      23.00+/-0.20  mag                      
4.82 hour       VT_B       43*70 sec      23.53+/-0.24  mag

Our photometry is in AB magnitude and not corrected for Galactic extinction.

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.