A Spatially Clustered Set of Short-Duration Fermi-GBM Subthreshold Transients Near SDSS DR7 Void #47/312

This technical note reports evidence for a statistically significant spatial clustering of short-duration gamma-ray transients detected in the Fermi-GBM subthreshold trigger catalog. Seven events occurring between 2020 and 2026 are concentrated near the sky position of SDSS DR7 void #47/312 in the Virgo–Coma region, with five events forming a compact core cluster. Under a uniform-sky null hypothesis, the observed clustering is unlikely to arise by chance prior to conservative trials considerations. The events share similar observational properties (short durations and hard spectra) and lack identified kilonova counterparts. The note provides event listings, sky-region definition, and basic significance estimates, and is intended to motivate independent analysis and follow-up searches for related transient activity in large-scale underdense environments.