TITLE: GCN CIRCULAR NUMBER: 40692 SUBJECT: Fermi GBM Sub-Threshold Detection of GRB 250610B DATE: 25/06/11 19:54:51 GMT FROM: rhamburg@usra.edu
R. Hamburg (USRA) reports on behalf of the Fermi-GBM Team:
The SVOM/ECLAIRs and SVOM/GRM instruments detected GRB 250610B on 2025-06-10T16:32:58 (GCN 40671). 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 data, identified a transient starting approximately 31 seconds after the SVOM/ECLAIRs trigger time, most significantly on the 16.384 s timescale and with a false alarm rate of 9.7e-5 Hz. Using the standard search protocol, the Targeted Search localization was found to be spatially consistent with the SVOM/ECLAIRs location. Additionally, the GBM Targeted Search transient was found with the highest significance using a "soft" spectrum (Band function with Epeak = 70 keV, alpha = -1.9, beta = -3.7) for a GRB. This is roughly consistent with the soft spectrum found by Wang et al. 2025 (GCN 40682).
[1] Goldstein et al. 2019 arXiv:1903.12597
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