TITLE: GCN CIRCULAR NUMBER: 38797 SUBJECT: GRB 250103B: SVOM detection of a long burst DATE: 25/01/03 16:30:29 GMT FROM: SVOM_group svomgroup@bao.ac.cn

T. Bouchet, D. Turpin (CEA), S. Guillot (IRAP), H. Goto (CEA), F. Daigne (IAP), L. Zhang (IHEP) report on behalf of the SVOM team:

The SVOM/ECLAIRs telescope triggered (sb25010303) at 2025-01-03T15:44:04.223 UTC (Tb) and located the long duration GRB 250103B also detected by Swift (Eyles-Ferris et al. GCN 38796).

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 7 alerts were received. The best detection is obtained by IMT with a signal-to-noise ratio of 10.6 in the 5-8 keV energy band over a time window of 41 s starting at Tb.

The localization of the best Alert is RA, Dec = 54.660, -33.769 (J2000). R.A. = 03:38:38.46 Dec = -33:46:09.67 The uncertainty on this position is 7.6 arcminutes at 90% C.L., which includes a systematic uncertainty of 2 arcminutes in quadrature.

The light curve shows a main single episode in the GRM data with a preliminary T90 duration of about 25 s below 550 keV. Further analysis will be conducted once the X-band telemetry data of ECLAIRs and GRM are received.

SVOM did not slew on this burst.

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: Tristan Bouchet (tristan.bouchet@cea.fr)

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