GRB 221009A or Swift J1913.1+1946: Fermi-LAT detection

At 14:17:05.99 on October, 09, 2022 Fermi-LAT detected high-energy emission from Swift J1913.1+1946 or GRB 221009A, which was reported by Swift (Dichiara et al. GCN #32632) and by GBM (Veres et al. GCN #32636). The best LAT on-ground location is found to be RA, Dec = 288.21, 19.73 (J2000) with an error radius of 0.09 deg (90 % containment, statistical error only). This was 94 deg from the LAT boresight at the time of the trigger. The 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. The 100 MeV - 1 GeV photon flux in the time interval 500-3500 s after the Swift trigger is (1.27 +/- 0.16)E-05 ph/cm2/s. The estimated photon index above 100 MeV is -2.12 +/- 0.11. The highest-energy photon is a 7.8 GeV which is observed 766 seconds after the Swift trigger. The Fermi-LAT point of contact for this burst is Elisabetta Bissaldi (elisabetta.bissaldi@ba.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.