TITLE: GCN CIRCULAR NUMBER: 45270 SUBJECT: GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst DATE: 26/08/02 10:09:19 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> Xin Feng (GXU), Hatsune Goto (RIKEN, CEA), Donghua Zhao (NAOC), Weinjin Xie (NAOC), Runchao CHEN (NJU), Feliu Lacreu (IAP), Diego Götz (CEA), report on behalf of the SVOM mission team: At 2026-08-02T09:23:10 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260802A (SVOM burst-id sb26080210). 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 Count-Rate Trigger (CRT), which produced a sequence of 3 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.09 in the [5-20] keV energy band starting at 2026-08-02T09:23:10. The localization of the best alert is R.A., Dec. 339.4431, 53.2195 degrees (J2000) with a 90% confidence level (C.L.) radius of 9.72 arcmin (including systematic error of 2 arcmin added in quadrature). The SVOM/ECLAIRs showed a single peak structure lasting about 0.2 seconds. We note that the magnetar EP J223759.5+531421(Atel #17859) is located in ECLAIRs error box, and given the short and soft nature of the burst, we suggest it is associated with this newly discovered magnetar. SVOM slewed to the burst. SVOM/MXT began observing the field at 2026-08-02T09:25:42 UTC, 151 seconds after T0. Using onboard processed data we found a possible uncatalogued X-ray source with a low SNR, located at R.A., Dec. 339.439, 53.234 degrees: R.A. (J2000) = 22h37m45s Dec. (J2000) = 53d14m02s with a 90% C.L. radius of 161 arcseconds. This location is 0.89 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received. VT began observing the field after the slew. The analysis of the data will be published in a future circular. 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 Wenjin Xie: xiewj@bao.ac.cn. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/45270. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...