{
  "eventId": "GRB 260919A",
  "circularId": 45794,
  "eventType": [
    "GRB",
    "Gamma-ray Transient",
    "X-ray Transient"
  ],
  "subject": "Fermi GBM Detection of GRB 260919A / EP260920a",
  "submitter": "rhamburg@usra.edu",
  "createdOn": 1790890064851,
  "submittedHow": "web",
  "body": "R. Hamburg (USRA), A. Trigg (NASA/MSFC), O. Mukherjee (USRA), and E. Burns (LSU) report on behalf of the Fermi-GBM Team:\n\nThe Einstein Probe WXT detected the fast X-ray transient EP260920a on 2026-09-20T00:06:04 UTC (GCN 45649).\n\nThe Fermi Gamma-ray Burst Monitor (GBM) Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified GRB 260919A, a bright and spatially-consistent transient with a duration of roughly 250 s. This GRB was detected most significantly at 2026-09-19T23:52:04.224 UTC, and was found on the 8.192 s timescale using a normal GRB spectrum (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3). The Targeted Search significance of GRB 260919A is well within the range of on-board triggers, but GRB 260919A occurred within the 10 min post-trigger interval after GBM trigger 260919992 / 811554497 during which further GBM triggering is disabled. \n\nGBM trigger 260919992 / 811554497 was detected at 2026-09-19T23:48:12.80, approximately 800 s before the EP trigger time, and was initially classified as a TGF by the flight software. It was subsequently classified as uncertain due to extreme localization uncertainties. The connection between GBM trigger 260919992 / 811554497 and GRB 260919A is currently uncertain.\n\nCombining the Targeted Search localization with the IPN localization (GCN 45792), we find the spatial association probability between GRB 260919A and EP260920a is 99% (0.9887). We note the large temporal offset of approximately 600 s. However, the spatial coincidence suggests a common origin between GRB 260919A and EP260920a.\n\n[1] Goldstein et al. 2019 arXiv:1903.12597\n",
  "format": "text/plain"
}