TITLE: GCN CIRCULAR NUMBER: 21127 SUBJECT: GRB 170522A: Fermi-LAT detection DATE: 17/05/23 01:46:11 GMT FROM: Judith Racusin at GSFC M. Arimoto (Waseda University) and J. L. Racusin (NASA/GSFC) report on behalf of the Fermi-LAT team: At 15:45:35.28 on May, 22, 2017 Fermi-LAT detected high-energy emission from GRB 170522A, which was also detected by Fermi-GBM (trigger 517160740 / 170522657, Stanbro et al., GCN 21126). The best LAT on-ground location is found to be RA, Dec = 139.34, 25.67 (J2000) with an error radius of 0.19 deg (90 % containment, statistical error only). This was 50 deg from the LAT boresight at the time of the trigger and triggered an autonomous repoint of the spacecraft. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the GBM trigger with high significance. The highest-energy photon is a 3.7 GeV event which is observed 8 seconds after the GBM trigger. A Swift ToO has been requested for this burst. The Fermi-LAT point of contact for this burst is Judith Racusin (judith.racusin@nasa.gov). 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.