GRB 240825A: Fermi-LAT detection

On Aug 25, 2024, Fermi-LAT detected high-energy emission from GRB 240825A, which was also detected by Fermi-GBM (trigger 746293985 / 240825662, GCN 37273) and Swift-BAT (Gupta et al., GCN 37274). The best LAT on-ground location is found to be: RA, Dec = 344.56, 1.04 (J2000) with an error radius of 0.07 deg (90 % containment, statistical error only). This was 52 deg from the LAT boresight at the time of the GBM trigger: T0 = 15:53:00 UT. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-2000 s after the GBM trigger is (2.9 +/- 0.2) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.65 +/- 0.09. The highest-energy photon is a 40 GeV event which is observed ~ 240 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Francesco Longo ( francesco.longo@ts.infn.it). The 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.