TITLE: GCN CIRCULAR NUMBER: 40862 SUBJECT: GRB 250628B: SVOM detection of a long burst DATE: 25/06/28 17:30:16 GMT FROM: SVOM_group svomgroup@bao.ac.cn
D. Dornic, J-G. Ducoin, J-L. Atteia, O. Godet, C. Plasse, report on behalf of the SVOM mission team:
At 2025-06-28T16:29:30 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250628B (SVOM burst-id sb25062804).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 6.90 in the [5-20] keV energy band over a time window of 20.48 seconds starting at 2025-06-28T16:29:10.
The localization of the best alert is R.A., Dec. 333.1563, -45.5663 degrees: R.A. (J2000) = 22h12m37.51s Dec. (J2000) = -45d33m58.52s with a 90% confidence level (C.L.) radius of 11.33 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a single/multiple broad/narrow peak structure with a T90 duration of about 33.51s (-3.02 +4.13).
Due to the detection significance being below the slew threshold, no immediate slew was performed on this burst. A SVOM ToO has been programmed for follow-up.
No X-ray observation could be performed by SVOM/MXT for the time being.No optical observation could be performed by SVOM/VT for the time being.
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 Dornic Damien: dornic@cppm.in2p3.fr. Please contact the BA by email if you require additional information.
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