TITLE: GCN CIRCULAR NUMBER: 45594 SUBJECT: GRB 260914A: SVOM/ECLAIRs refined analysis DATE: 26/09/16 13:26:51 GMT FROM: SVOM_group M. Brunet (IRAP), N. Dagoneau (CEA), O. Godet (IRAP), C. Wang (IHEP), W. Xie (NAOC) report on behalf of the SVOM/ECLAIRs team: Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260914A (SVOM burst-id sb26091401 – GCN 45562, trigger time T0 = 2026-09-14T11:12:31 UTC), which was also detected by Fermi/GBM as a sub-threshold (Hamburg, GCN 45569). The burst that triggered ECLAIRs onboard shows a main broad peak from T0-2.2 s to T0+8.3 s seen below 50 keV and a soft precursor from T0-10.4 s to T0-8.8 s seen below 20 keV. The burst duration estimated through the imaging technique is T90 = 15.5 -7.2/+1.5 s in the 4-120 keV energy band. The time-averaged spectrum from T0-2.2 s to T0+8.3 s in the 5-120 keV energy range is best fitted by a powerlaw model, with alpha = -1.98 +/-0.07. With this model, the 4-120 keV fluence is (1.68 +/-0.11)e-6 erg/cm^2 and the 4-120 keV photon flux is 7.0 +/-0.3 ph/cm^2/s. Using a band model with alpha = -1 and beta = -2.5 (fixed) also gives a good fit with Epeak = 14.2 +2.0/-1.8 keV. With this model, the 4-120 keV fluence is (1.43 +/-0.08)e-6 erg/cm^2 and the 4-120 keV photon flux is 6.5 +/-0.3 ph/cm^2/s. Assuming a redshift of z=0.778 (Saccardi et al., GCN 45579, Yang et al., GCN 45582), a standard cosmology with H_0 = 67.3 km/s/Mpc and Omega_M = 0.315 (Planck Collaboration, 2014) and the previous band model with Epeak = 14.2 keV, we estimate the isotropic energy release E_iso is about 3.6 e51 erg. With these estimates, GRB 260914A appears close to the Ep,z and E_iso ranges distribution of Type II (collapsar-like) GRBs on the Amati relation reported by Willingale et al. 2017. 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: Nicolas Dagoneau (nicolas.dagoneau at cea.fr)