GCN Circular 41405
Subject
GRB 250818B: SVOM detection of a short burst
Event
Date
2025-08-18T04:00:21Z (7 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
Z. Q. Wang (GXU), Y. F. Liang (PMOC), W. J. Xie, D. H.Zhao (NAOC), F. Robinet (IJCLab), L. Zhang (IHEP), report on behalf of the SVOM mission team:
At 2025-08-18T03:29:09 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250818B (SVOM burst-id sb25081801).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.74 in the [5-20] keV energy band over a time window of 2.50 seconds starting at 2025-08-18T03:29:08.
The localization of the best alert is R.A., Dec. 46.0666, -3.1784 degrees:
R.A. (J2000) = 3h04m15.99s
Dec. (J2000) = -3d10m42.10s
with a 90% confidence level (C.L.) radius of 7.44 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2025-08-18T03:29:08 on a timescale of 1 seconds with an SNR of 6.80.
https://www.bursthub.cn//admin/static/svgrb250818B.png
SVOM slewed to the burst. However, the MXT was occulted by the Earth. The burst localization results will be published later in another GCN circular.
A SVOM ToO has been programmed for follow-up.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Ziqi.Wang: ziqi.wang@st.gxu.edu.cn.
Please contact the BA by email if you require additional information.