TITLE: GCN CIRCULAR NUMBER: 40513 SUBJECT: GRB 250521B: SVOM detection of a burst through offline search DATE: 25/05/21 16:50:38 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> A. Foisseau, C. Lachaud (APC), M. Brunet (IRAP), N. Dagoneau (CEA) report on behalf of the SVOM team: The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 250521B, starting at 2025-05-21T04:19:17.8 UTC (Tb), through an offline search with the event-by-event data downloaded through the X-band ground station. The burst was detected within several energy ranges in a 5.12 seconds timescale. The best detection is obtained by the image trigger with a signal-to-noise ratio of 7.2 within 8-50 keV over a time window of 5.12 seconds starting at Tb. The lightcurve consists of a single pulse lasting around 5s. The localization of the source is RA, Dec = 200.822, 1.766 degrees: RA (J2000) = 13h23m17.3s Dec (J2000) = 01d45m57.6s with a 90% C.L. radius of 12.2 arcmin (including systematic error of 6 arcmin added in quadrature). We note that no bright X-ray sources are found in the error box. 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. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP. The SVOM point of contact for this event is : A. Foisseau : foisseau@apc.in2p3.fr Please contact him by email if you require additional information regarding the SVOM follow-up of this burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/40513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...