GCN Circular 41894
Subject
GRB 250919A/EP250919a: SVOM/VT optical observation
Event
Date
2025-09-20T02:42:26Z (4 days ago)
From
Yinuo Ma <mayn@bao.ac.cn>
Via
Web form
Y. N. Ma, L. P. Xin, Z. H. Yao, Y. L. Qiu, C. Wu, H. L. Li, 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) report on behalf of the SVOM/VT team.
SVOM performed a Target of Opportunity observation of GRB 250919A/EP250919a detected by Fermi/GBM, SVOM/GRM, EP/WXT, NuSTAR, and Glowbug (Fermi GBM team GCN 41874; Wang et al., GCN 41882; Liang et al., GCN 41879; Waratkar & Grefenstette, GCN 41888; Cheung et al., GCN 41891). SVOM/VT began observing the field at 2025-09-19T14:24:05 UTC, 13.92 hours after the trigger, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With X-band data available, the optical counterpart (Li et al., GCN 41877; Levan et al., GCN 41883; Oates et al., GCN 41886; Lipunov et al., GCN 41893) was clearly detected in both VT_B and VT_R bands. The magnitudes are:
mid time (h) | exposure time (s) | band | mag (AB) | mag err
-------------|-------------------|------|----------|--------
14.240 | 47*50 | VT_B | 18.55 | 0.02
14.247 | 46*50 | VT_R | 18.13 | 0.02
Our photometry was 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.