TITLE: GCN CIRCULAR NUMBER: 30125 SUBJECT: Fermi GBM Sub-Threshold Detection of new Swift SGR J1555.2-5402 DATE: 21/06/04 17:34:43 GMT FROM: Cori Fletcher at USRA C. Fletcher (USRA) reports on behalf of the Fermi-GBM Team: Swift-BAT detected Swift SGR J1555.2-5402 at 09:45:46 UT (GCN 30120). 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 was run from +/-30 s around the BAT trigger time. A transient source was identified whose most significant timescale according to the automated search is 64 ms, with a false alarm rate of 5.8e-05 Hz and a location consistent with the Swift-BAT event, using the standard search protocol with a S/N of 6. The event was found to be even more significant (S/N of 12) on the 8 ms timescale, but an associated false alarm rate is currently not available on the 8 ms timescale. 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). [1] Goldstein et al. 2019 arXiv:1903.12597