GCN 44210: GRB 260330B: SVOM/ECLAIRs refined analysis

Authors: S. Guillot, M. Brunet, F. Triot, H. Yang, O. Godet, G. Lan (IRAP) 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 260330B (SVOM burst-id sb26033003 – GCN 44157, trigger time T0 = 2026-03-30T14:19:57 UTC), which was also detected by Fermi GBM as a sub-threshold event (GCN 44159).

The burst that triggered ECLAIRs onboard shows a multiple-peak lightcurve. The burst duration is T90 = 58.7 (+9.4)(-4.9) s s in the 4-120 keV energy band.

The time-averaged spectrum from T0-23.0 s to T0+43.04 s in the energy range 4-120 keV is best fitted by a cutoff powerlaw model with alpha = -1.21 (+0.18)(-0.170), with Epeak = 24.9 (+11.5)(-8.8) keV. With this model, the 4-120 keV fluence is 1.32 (0.02)(-0.32) e-6 erg/cm^2 and the 4-120 keV photon flux is 0.85 +0.01/-0.14 ph/cm^2/s. 

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: Sebastien Guillot (IRAP) (sebastien.guillot1 at utoulouse.fr)