TITLE: GCN CIRCULAR NUMBER: 40374 SUBJECT: GRB 250507A: SVOM detection of a long burst DATE: 25/05/07 07:23:04 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> Z. Wang (GXU), Y. Liang (PMO), H. Yang, O. Godet (IRAP), P. Maggi (ObAS), D. Götz (CEA), L Xin (NAOC) report on behalf of the SVOM mission team: SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250507A (SVOM burst-id sb25050703) starting at 2025-05-07T06:34:45.17 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 the Count-Rate Trigger (CRT) and Image Trigger (IMT). A sequence of 10 alerts was produced. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 10.65 in the 8-120 keV energy band over a time window of 40.96 seconds starting at Tb. The localization of the best alert is R.A., Dec. 182.990, -23.615 degrees: R.A. (J2000) = 12h11m57.6s Dec. (J2000) = -23h36m54s with a 90% confidence level (C.L.) radius of 7.5 arcmin (including systematic error of 2 arcmin added in quadrature). SVOM slewed to the burst. MXT began observing the field after the slew, starting at 2025-05-07T06:41:02 i.e. 377 s after Tb. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec 183.074, -23.598 degrees: R.A. (J2000) = 12h12m17.76s Dec. (J2000) = -23d35m52.8s with a 90% C.L. radius of 30 arcseconds (including 25 arcseconds systematic error added in quadrature). This location is 4.7’ 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 recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments. 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. The Burst Advocate (BA) on shift for this burst is Ziqi Wang: ziqi.wang@st.gxu.edu.cn. Please contact the BA 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/40374. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...