TITLE: GCN CIRCULAR NUMBER: 40707 SUBJECT: sb25061207: SVOM/VT optical counterpart DATE: 25/06/12 15:40:31 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), L. Zhang (IHEP), Y.-D. Hu (GXU), X.-L. Chen (YNU) report on behalf of the SVOM mission team
SVOM performed an automatic slew on the burst (sb25061207) triggered by SVOM/ECLAIRs (Zhang et al., GCN 40697). SVOM/VT began observing the field at 2025-06-12T10:30:44 UTC, 202 seconds after Tb, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
A candidate is found using VT X-band data, compared to Legacy survey, within the error box of SVOM/Eclairs (Zhang et al., GCN 40697) at R.A., Dec 198.09415, +0.07508 degrees:
RA (J2000) = 13:12:22.597 Dec (J2000) = +00:04:30.28
with an uncertainty of 0.5 arcsec. The source is detected in both VT_R and VT_B bands. With the data available, the light curve shows that this source was fading at first time, and then rebrightening to the peak of VT_R ~ 18.0 mag at around 1000 seconds after the trigger time, and then decayed.
mid-time | exposure time | band | mag (AB) ------------ |----------------- |------------------- 1.79 hour | 50 sec | VT_B | 21.6+/-0.2 1.79 hour | 50 sec | VT_R | 20.8+/-0.1
Given the VT colour of the candidate, it might be a low redshift transient.
We also noticed that there is a faint blue source at the Legacy survey image at the location of the candidate, which might be the host.
More followups are encouraged.
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 Y.-D. Hu : hyd@gxu.edu.cn.
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