TITLE: GCN CIRCULAR NUMBER: 19836 SUBJECT: GRB 160821A: Fermi-LAT refined analysis DATE: 16/08/22 06:01:24 GMT FROM: Makoto Arimoto at Tokyo Inst of Tech M. Arimoto (Waseda U./Tokyo Tech), M. Axelsson (KTH Stockholm), F. Dirirsa (U. Johannesburg) and F. Longo (INFN/Trieste) report on behalf of the Fermi-LAT team: We report the on-ground localization and analysis of GRB 160821A, which triggered an onboard LAT detection (McEnery et al., GCN 19831). All times are relative to the initial GBM trigger (Stanbro et al., GCN 19835). The best LAT on-ground location is found to be: RA, Dec = 171.3, 42.3 deg (J2000) with an error radius of 0.08 deg (90 % containment, statistical error only). This is fully compatible with the position of the prompt emission detected by Swift/BAT (Siegel et al., GCN 19830). This was 17 deg from the LAT boresight at the time of the GBM trigger and triggered an autonomous repoint of the spacecraft. More than 50 photons above 100 MeV and 4 photons above 1 GeV were detected within 245s, before the spacecraft entered the SAA. The GRB did not come back into the Fermi-LAT FoV until T0 + 1380s. The LAT emission was coincident with the bright pulse observed by GBM at ~T0+135 s. The highest-energy photon is a 4.7 GeV event which is observed ~212 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Francesco Longo (francesco.longo@trieste.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.