GCN Circular 44397
Subject
GRB 260421B: SVOM/ECLAIRs refined analysis
Event
Date
2026-04-23T10:06:59Z (a day ago)
Edited On
2026-04-23T15:36:19Z (17 hours ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet (IRAP), L. Delfosse (CEA), O. Godet (IRAP), S. Schanne (CEA), W. L. Zhang (PMO), Z. Y. 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 260421B (SVOM burst-id sb26042105 – GCN 44362, trigger time T0 = 2026-04-21T04:13:25 UTC), which was also detected by Fermi (GCN 44360, 44361, 44382) and SVOM/GRM (GCN 44389).
The burst that triggered ECLAIRs onboard shows a multiple peak lightcurve. The burst duration is T90 = 26.3 +4.4/-6.0 s in the 4-120 keV energy band.
The time-averaged spectrum from T0-12 s to T0+20 s in the energy range 5-120 keV is best fitted (chi²/dof = 20.1/16) by a broken powerlaw model with best-fit parameters: alpha = -1.00 +0.35/-0.11, beta = -1.42 +0.07/-0.06 and a break energy of 13.7 +2.7/-4.4 keV. With this model, the 4-120 keV fluence is (8.6 +0.1/-1.1)e-6 erg/cm^2 and the 4-120 keV photon flux is 6.4 +0.1/-0.7 ph/cm²/s.
Using a simple powerlaw provides a bad fit (chi²/dof = 31.3/18).
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: Marius Brunet (IRAP) (marius.brunet at utoulouse.fr)