GCN Circular 46117
Subject
GRB 261029A: SVOM/ECLAIRs refined analysis
Event
Date
2026-10-30T21:20:44Z (2 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, O. Godet, J.-L. Atteia (IRAP), A. Coleiro (APC), Y. Liang (PMO), Z. Liu (GZNU) 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 261029A (SVOM burst-id sb29102901 – Goto et al., GCN 261029A, trigger time T0 = 2026-10-29T01:27:07 UTC), which was also detected by Fermi/GBM (Fermi GBM team, GCN 46071, and Scotton et al., GCN 46098), Fermi/LAT (Longo et al., GCN 46085), AstroSat/CZTI (Salunke et al., GCN 46089), CALET Gamma Ray Burst Monitor (Marrocchesi et al. GCN 46095), SVOM/GRM (Yu et al., GCN 46096), NuSTAR (Waratkar et al., GCN 46100), GECAM-B (Yu et al., GCN 46108) and Glowbug (Cheung et al., GCN 46112).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 47.5 +1.0/-0.9 s in the 4-120 keV energy band.
The refined burst localization is RA, Dec = 8.827, 34.533 degrees :
RA (J2000) = 00h35m18.5s
Dec (J2000) = 34d31m58.8s
with a 90% C.L. radius of 2.31 arcmin (including systematic error of 2 arcmin added in quadrature).
This position is 2.01 arcmin from the afterglow position determined by GOTO (O’Neill et al., GCN 46073).
The time-averaged spectrum from T0-0.15s s to T0+47.34s s in the 5-120 keV energy range is best fitted by a powerlaw + blackbody model (chi²/dof = 40/26 ). The photon index is alpha = -1.10 +/-0.03 and the blackbody temperature is 1.42 +/-0.17 keV. With this model, the 4-120 keV fluence is (2.34+/-0.04)e-5 erg/cm^2 and the 4-120 keV photon flux is 10.4 +/- 0.1 ph/cm^2/s.
Using a simple powerlaw does not give a good fit (chi²/dof = 83.8/28).
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: M. Brunet (IRAP) (marius.brunet at utoulouse.fr)