GCN Circular 45586
Subject
GRB 260915A: SVOM/VT refined early optical upper limits
Event
Date
2026-09-15T13:53:44Z (4 days ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. N. Ma, C. Wu, L. P. Xin, Y. L. Qiu, Z. H. Yao, J. R. Xu, L. J. Chen, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
With more early SVOM/VT X-band data available, the refined analysis yields an early optical upper limits for GRB 260915A (Liang et al., GCN 45570; Hamburg et al., GCN 45574) within the error box of the EP-FXT's source 1 (Shi et al., GCN 45585) and SVOM/MXT (Liang et al., GCN 45570).
Mid-time（t-T0）| Band | Exposure Time | 3-sigma upper limit
16.4 min VT_B 32*50 sec > 23.3 mag
18.3 min VT_R 30*50 sec > 23.2 mag
The above measurements are in the AB magnitude and are not corrected for Galactic extinction.
The result is consistent with the non-detections from SVOM/VT (Wu et al., GCN 45575；Li et al., GCN 45581), LCO (Yin et al., GCN 45573), NOT (Zhu et al., GCN 45577), GTC (Perez-Garcia et al., GCN 45578), and SVOM/COLIBRÍ (Ducoin et al., GCN 45580) and REM (Brivio et al., GCN 45584).
We notice that EP-FXT's source 2 is overlapped with a Quasar (SDSS J003224.91+081258.0).
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.