TITLE: GCN CIRCULAR NUMBER: 19831 SUBJECT: GRB 160821A: Fermi-LAT detection of a bright burst DATE: 16/08/21 21:40:46 GMT FROM: Julie McEnery at NASA/GSFC **J. McEnery, J. Racusin (NASA/GSFC) and Francesco Longo (INFN/Trieste) report on behalf of the Fermi-LAT team: At 20:36:44.33 on August 21, 2016, Fermi-LAT triggered on high-energy emission from GRB 160821A, also detected by GBM (trigger 493504474/ GRB160821857), and Swift-BAT (Siegel et al., GCN 19830). The onboard location is RA, Dec = 172.5, 43.0 (J2000) with an error radius of 0.5 deg (90% containment, systematic error only). This was 17 deg from the LAT boresight at the time of the trigger. Onboard LAT GRB detections are relatively rare, and imply that this GRB is exceptionally bright at high energy gamma-rays. We strongly encourage follow-up observations. 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.