GCN Circular 42887
Subject
GRB 251129A / EP251129a: SVOM/VT optical fading
Event
Date
2025-11-29T05:41:54Z (2 days ago)
Edited On
2025-12-01T04:53:50Z (10 hours ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li , L. P. Xin, Y. L. Qiu, C. Wu, Z. H. Yao, Y. N. Ma, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA), W. J. Tan (IHEP), D. F. Kong (GXU) report on behalf of the SVOM/VT team.
SVOM/VT performed an automatic slew to GRB 251129A/EP251129a triggered by SVOM/ECL (sb25112901, Tan et al., GCN 42879). The burst was also triggered by EP (Wu et al., GCN 42884). SVOM/VT began the observation at 2025-11-29T02:43:03 UTC, i.e., 658 seconds post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
With the downloaded early X band data, the optical counterpart (Angulo et al. GCN 42880; Watson, GCN 42883; Wu et al., GCN 42882; Masi et al. GCN 42885) was clearly detected in both channels. The measurements are given below:
Mid_time Band Exposure Time Magnitude (AB)
12.43 min VT_B 50 sec 18.16+/-0.03 mag
12.43 min VT_R 50 sec 17.89+/-0.03 mag
44.96 min VT_B 50 sec 19.11+/-0.04 mag
44.96 min VT_R 50 sec 18.80+/-0.03 mag
It was fading with a slope of about 0.7 with a single power law.
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.