TITLE: GCN CIRCULAR NUMBER: 40671 SUBJECT: GRB 250610B: SVOM detection of a long burst DATE: 25/06/10 17:27:30 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> A. Saccardi, J. Rodriguez, N. Dagoneau (CEA), C. Van Hove (IJCLab) report on behalf of the SVOM mission team. At 2025-06-10T16:32:58 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250610B (SVOM burst-id sb25061018). 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 40 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 30.55 in the [8-50] keV energy band over a time window of 81.92 seconds starting at 2025-06-10T16:33:19. The localization of the best alert is R.A., Dec. 200.1831, 31.1028 degrees: R.A. (J2000) = 13h20m43.94s Dec. (J2000) = 31d06m10.04s with a 90% confidence level (C.L.) radius of 3.22 arcmin (including systematic error of 2 arcmin added in quadrature). The ECLAIRs light curve may show a double narrow peak structure with a T90 duration of about 134.368 (-13.465 +23.518) s. The ECLAIRs peak count rate was ~496.6503 ± 191.3858 counts/sec in the band [20-50] keV, ~5.6 seconds after the trigger. This burst was also detected by SVOM/GRM with a significance of 14.30. The GRM light curve showed a single broad peak structure with a T90 duration of about 69.237 (-6.343 +6.558) s. The GRM peak count rate was ~470.4469 ± 82.6942 counts/sec in the band [4-5000] keV, ~34.4 seconds after the trigger. A SVOM ToO has been executed for follow-up and started to observe at 2025-06-10T16:59 UTC. 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Andrea Saccardi: andrea.saccardi@cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/40671. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...