TITLE: GCN CIRCULAR NUMBER: 38787 SUBJECT: GRB 250103A: SVOM detection of a long burst DATE: 25/01/03 11:16:17 GMT FROM: SVOM_group svomgroup@bao.ac.cn

Y. Wang (PMO, CAS), J-X. Cao (GXU), 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 and located the long duration GRB 250103A (sb25010301) starting at 2025-01-03T09:56:33.551 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 18 alerts were received. The best detection is obtained by CRT with a signal-to-noise ratio of 18.6 in the 8-50 keV energy band over a time window of 20 s starting at Tb. The localization of the best Alert is RA, Dec = 22.083, -5.096 (J2000). The statistical uncertainty on this position is 4.6 arcminutes, which includes a systematic uncertainty of 2 arcminutes in quadrature.

The light curve shows multiple broad peaks in 5-120 keV in ECLAIRs and below 550 keV in GRM with a preliminary T90 duration greater than 250 s (5-120 keV).

The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250103A.png

SVOM slewed automatically on this burst.

MXT began observing the field at 2025-01-03T10:12:28 UTC, 955 seconds after Tb. No X-ray afterglow candidate has been detected in the MXT field of view by the on-board software. Further analysis will be conducted once the X-band telemetry data are received.

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: Yun Wang (wangyun@pmo.ac.cn)

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