GCN Circular 45639

A. Jameson (UAH) reports on behalf of the Fermi-GBM Team:

SVOM ECLAIRs detected the GRB 260918A on 2016-09-18 at 03:47:36 UTC (GCN 45619). 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 starting approximately 14 seconds after the ECLAIRs best image SNR time of 2026-09-18T03:47:15 UTC. The Targeted Search candidate was found most significantly on the 2.048 s timescale, with a false alarm rate of 1.3e-4 Hz. The Fermi-MET of the start time of this transient is 811396053.676 s. The Targeted Search localization has a spatial association probability of 71.3%, but has large uncertainties due to the weak nature of the transient.

Additionally, the GBM Targeted Search event was found with the highest significance using a "hard" spectrum (Comptonized function with Epeak = 1500 keV, alpha = -0.5) for a GRB.

The Targeted Search data release product for this event can be found here: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/targeted_search/trigger_report.php?trigger_id=811396040&sample=SVOM_GCNs&hash=e9806eaf891b7de8

[1] Goldstein et al. 2019 arXiv:1903.12597