GCN 44159: Fermi GBM Sub-Threshold Detection of GRB 260330B

A.C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi-GBM Team:

SVOM/ECLAIRs detected GRB 260330B on 2026-03-30 at 14:19:57 UTC (GCN 44157). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no candidates.

The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient approximately 16 s after the ECLAIRs best image SNR time of 2026-03-30T14:19:31. The Targeted Search candidate was found most significantly on the 32 s timescale using the "soft" spectral template (i.e., Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) and has a false alarm rate of 1.0-04 Hz. The Fermi-MET of this transient is 796573176.806 s. The Targeted Search localization is spatially consistent with the ECLAIRs location.
 
[1] Goldstein et al. 2019 arXiv:1903.12597