GCN Circular 38845

W. Zheng (UCB), Z-Q. Wang (GXU), W.-J. XIE (NAOC, CAS), D.-H. ZHAO (NAOC,
CAS), S. Guillot (IRAP), D. Götz (CEA), H. Goto (CEA), C-W. Wang (IHEP)
report on behalf of the SVOM team.

The SVOM/ECLAIRs telescope triggered and located the long duration GRB
250108A (sb25010802) starting at 2025-01-08T04:37:01.513 UTC (Tb).

The following trigger information was received on the ground with
low-latency by the SVOM VHF Alert Network.

The burst was detected by both the on-board Count-Rate Trigger (CRT) and
Image Trigger (IMT) and 9 alerts were received. The best detection is
obtained by IMT with a signal-to-noise ratio of 10.2 in the 5-8 keV energy
band over a time window of 40.96 s starting at Tb. The light curve in
ECLAIRs with a preliminary T90 duration is about 40 s.

The localization of the best Alert is RA, Dec = 207.946, 26.204 (J2000).
The uncertainty on this position is 7.79 arcminutes at 90% C.L. which
includes 2 arcminutes of systematic uncertainty in quadrature.

The SVOM/GRM light curve can be found here:

https://www.bursthub.cn//admin/static/svgrb250108A.png

SVOM performed an automatic slew and MXT started observing the ECLAIRs
error box at 04:40:49 UTC, i.e. 228 s after Tb. An uncatalogued X-ray
source has been found by the on board software at R.A., Dec. = 207.906,
26.232 (J2000) (13:51:38, +26:13:56, J2000) with an uncertainty of 60 arc
sec (90% C.L., including systematics). This source is located at 2.7 arc
minutes from the ECLAIRs position.

VT results will be reported later.

The Space 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.



The SVOM point of contact for this burst is: Weikang Zheng (
weikang@berkeley.edu)