TITLE: GCN CIRCULAR NUMBER: 41869 SUBJECT: GRB 250912A: SVOM/ECLAIRs refined analysis DATE: 25/09/18 15:09:27 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> Hui Yang, Olivier Godet, Marius Brunet, Jean-Luc Atteia (IRAP), Floriane Cangemi (APC), Jean-Grégoire Ducoin, Damien Dornic (CPPM) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 250912A (SVOM burst-id sb25091206, GCN 41820) detected at T0 = 2025-09-12T21:06:24.69, which was also detected by SVOM/GRM (GCN 41826) and Fermi/GBM (GCN 41819). The burst that triggered ECLAIRs consists of a short main peak starting from T0-1.19 s and lasting about 0.6 s in the 4-120 keV energy band, followed by extended emission continuing until T0+18.3 s. We note a weak precursor at T0-11.1 s, detected mainly in the 8-20 keV band by ECLAIRs and also by GRM, whose position is consistent with that of the main event. The spectrum of the main peak (from T0-1.19 s to T0-0.55 s) in the 4-120 keV energy range is well fitted by a power-law model with a photon index of 1.2 +/-0.2. With this model, the 4-120 keV flux is (1.7+/-0.4)e-07 erg/cm^2/s. The spectrum of the extended emission following the main peak (from T0-0.55 s to T0+18.31 s) in the 4-120 keV band is well fitted by a power-law model with a photon index of 1.4+/-0.1, yielding a 4-120 keV flux of (3.3+/-0.5)e-08 erg/cm^2/s. The spectral index is consistent with that measured by SVOM/GRM and Fermi/GBM (GCN 41828). The combined fluence of both components in the 4-120 keV is (7.3+/-1.0)e-07 erg/cm^2. The low count rates prevent a spectral analysis of the precursor and the time-resolved spectral analysis of the burst. All the quoted errors are at the 68% confidence level. 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. The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang@irap.omp.eu). View this GCN Circular online at https://gcn.nasa.gov/circulars/41869. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...