TITLE:   GCN CIRCULAR
NUMBER:  42141
SUBJECT: GRB 251006B/EP251006a: SVOM/VT optical candidate
DATE:    25/10/07 14:11:15 GMT
FROM:    Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>

L. P. Xin, H. L. Li, Y. L. Qiu, C. Wu, Z. H. Yao, 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), Z. Q. Wang, K. Liu (GXU) report on behalf of the SVOM/VT team.

SVOM/VT conducted ToO follow-up observations of GRB 251006B / EP251006a (Fermi GBM Team, GCN 42131; Yin et al. GCN 42137;  Wang et al., GCN 42139). The observation started on 2025-10-07T09:37:56 UT (i.e. 13.56 hour after Fermi trigger time) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channel simultaneously. 

Within the error box of EP-FXT source 2 (Yin et al., GCN 42140), an uncatalogued source was detected, compared to the Legacy survey. The position is at R.A., Dec. = 40.518487, -6.034955 degrees, equivalent to:
R.A. (J2000) =  02:42:04.43
Dec. (J2000) =  -06:02:05.8
with an uncertainty of 0.5 arcsec.

The magnitudes of the candidate are given below:

  Mid_time        Band        Exposure Time       Magnitude (AB)
13.5672  hour     VT_B          41*70 sec         22.37+/-0.11 mag                      
13.5672  hour     VT_R          39*70 sec         22.12+/-0.12 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.