{
  "submitter": "chiara.bartolini-1@unitn.it",
  "body": "E. Bissaldi (Politecnico and INFN Bari), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), A. Holzmann Airasca (UniTrento and INFN Bari), C. Bartolini (UniTrento and INFN Bari) and F. Longo (University and INFN, Trieste) report on behalf of the Fermi-LAT team:\n\nAt 10:17:17.29 UT on December, 08, 2025 Fermi-LAT detected high-energy emission from GRB 251208B, which was also detected by Fermi-GBM (trigger 786881842 / 251208429, GCN #43028) and Swift/BAT-GUANO (GCN #43033).\n\nThe best LAT on-ground location is found to be\n\nRA, Dec = 228.48, 29.07 (J2000)\n\nwith an error radius of 0.07 deg (90 % containment, statistical error only), which is consistent with the Swift/BAT-GUANO localization.\n\nThis was 39 deg from the LAT boresight at the time of the trigger.\n\nThe data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance.\nThe photon flux above 100 MeV in the time interval 0 - 1 ks after the GBM trigger is (3.13 ± 0.09)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.01 ± 0.23. The highest-energy photon is a 17 GeV event which is observed 419 seconds after the GBM trigger.\n\nA Swift ToO has been approved for this burst.\n\nThe Fermi-LAT point of contact for this burst is Chiara Bartolini (chiara.bartolini@ba.infn.it).\n\nThe Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.",
  "createdOn": 1765219908863,
  "submittedHow": "web",
  "bibcode": "2025GCN.43034....1B",
  "format": "text/plain",
  "subject": "GRB 251208B: Fermi-LAT detection",
  "circularId": 43034,
  "eventId": "GRB 251208B"
}