TITLE: GCN CIRCULAR NUMBER: 30421 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 210708A DATE: 21/07/08 16:52:18 GMT FROM: Cori Fletcher at USRA C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team: Swift-BAT detected GRB 210708A at 02:25:37 UT (GCN 30413). There was no Fermi-GBM onboard trigger around the event. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified no counterparts. The GBM targeted search [1], the most sensitive, coherent search for GRB-like signals identified a transient most significantly on the 4.096 s timescale, with a false alarm rate of 1.7e-04 Hz and a location consistent with the Swift-BAT event, using the standard search protocol with a S/N of 6. The GBM targeted search event was found with the highest significance with a "soft" spectrum (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. [1] Goldstein et al. 2019 arXiv:1903.12597