TITLE:   GCN CIRCULAR
NUMBER:  44072
SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 260321A
DATE:    26/03/21 22:15:38 GMT
FROM:    rhamburg@usra.edu

R. Hamburg (USRA) reports on behalf of the Fermi-GBM Team:

SVOM/ECLAIRs detected GRB 260321A on 2026-03-21 at 18:12:08 UTC (GCN 44071). 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 10 s after the ECLAIRs best image SNR time of 2026-03-21T18:11:48. The Targeted Search candidate was found most significantly on the 8 s timescale using the "normal" spectral template (i.e., Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) and has a false alarm rate of 3.7e-04 Hz. The Fermi-MET of this transient is 795809523.353 s. The Targeted Search localization is spatially consistent with the ECLAIRs location.
 
[1] Goldstein et al. 2019 arXiv:1903.12597