TITLE: GCN CIRCULAR NUMBER: 42781 SUBJECT: GRB 251103A: SVOM/ECLAIRs and SVOM/GRM joint refined analysis DATE: 25/11/20 09:43:04 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> N. Dagoneau, B. Hubert, S. Schanne (CEA), J.-L. Atteia (IRAP), C.-W. Wang (IHEP) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs and SVOM/GRM observations of GRB 251103A (SVOM burst-id sb25110301, GCN 42534, GCN 42552), which was also detected by NOT (GCN 42535), Fermi/GBM (GCN 42536), LCO (GCN 42538), BOOTES-2/TELMA (GCN 42539), GOTO (GCN 42543), SVOM/COLIBRI (GCN 42549), Swift-XRT (GCN 42551), Fermi/GBM (GCN 42553), Swift/UVOT (GCN 42554), Kilonova-Catcher (GCN 42559), WINTER (GCN 42562), Global MASTER-Net (GCN 42565), Swift/BAT-GUANO (GCN 42568), KAIT (GCN 42571), Insight-HXMT (GCN 42572), Xinglong 2.16m (GCN 42573), OHP/T193 (GCN 42574), WFST (GCN 42577), ZTF (GCN 42579) The burst that triggered ECLAIRs shows a light-curve consisting of two peaks: a soft precursor occurring from T0-4s to T0+2s mainly in the 4-30 keV energy band (T0=2025-11-03T04:46:21 UTC), and a main peak occurring from T0+2s to T0+16s in the 4-120 keV energy band. The event has a total duration of 20s (T90 is not a good measure in this case, because it covers incompletely both peaks). ECLAIRs triggered onboard on both peaks, GRM only detected the main peak. Using an analysis of the ECLAIRs data alone, the time-averaged spectrum of the precursor (from T0-4 s to T0+2 s) in the 8-20 keV energy band is best fitted by a power-law model with a photon index of -3.01 -0.2/+0.3, indicating a very soft spectrum (while a simple black-body model does not provide a good fit). With this model, the mean energy fluence in 4-120 keV is (4.97 +/- 2.73)E-08 erg/cm^2. The time-averaged spectrum of the main peak (from T0+2 s to T0+16 s) in the 8-120 keV energy band is best fitted by a cutoff power-law model with a photon index of -1.18 -0.02/+0.12 and a cutoff energy parametrized as Epeak of 122 +/- 26 keV. With this model, the mean energy fluence in 4-120 keV is (4.14 +/- 0.19)E-06 erg/cm^2. Using a joint analysis of ECLAIRs and GRM data, the time-averaged spectrum of the main peak (T0+2 s to T0+16 s) in the 8-1000 keV energy band is best fitted by a Band model with a low-energy photon index of -1.12 +/-0.04, a high-energy photon index of -2.04 -0.11/+0.08 and a cutoff energy parametrized as Epeak of 116 +/- 23 keV. With this model, the mean energy fluence in 10-1000 keV is (8.33 +/- 0.58)E-06 erg/cm^2. With a redshift of z = 0.76 (GCN 42540), the isotropic equivalent energy of this burst Eiso (from 1 keV to 10 MeV in its rest frame) is 2.01 +/- 0.14 10^52 erg, which makes this GRB consistent with type II GRBs in the 'Amati' relation diagram (Amati et al. 2002). 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 point of contact for this burst is: Nicolas Dagoneau (nicolas.dagoneau AT cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/42781. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...