GRB 240828A: Fermi-LAT detection

On Aug 28, 2024, Fermi-LAT detected high-energy emission from GRB 240828A, which was also detected by Fermi-GBM (trigger 746549711 / 240828622, GCN 37317), and AstroSat CZTI (GCN 37328). The best LAT on-ground location is found to be: RA, Dec = 225.49, 36.64 (J2000) with an error radius of 0.30 deg (90 % containment, statistical error only). This was 93 deg from the LAT boresight at the time of the GBM trigger: T0 = 14:55:06 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 3500-6100 s after the GBM trigger is (8.2 +/- 3.8) E-7 ph/cm2/s. The estimated photon index above 100 MeV is -2.1 +/- 0.4. The highest-energy photon is a 1.7 GeV event which is observed ~ 5400 seconds after the GBM trigger. A Swift ToO has been approved for this burst. The Fermi-LAT point of contact for this burst is Niccolo' Di Lalla ( niccolo.dilalla@stanford.edu). 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.