TITLE: GCN CIRCULAR NUMBER: 21380 SUBJECT: GRB 170728B: Fermi-LAT detection DATE: 17/07/29 13:03:36 GMT FROM: Manal Yassine at IN2P3/LUPM/CNRS M. Yassine (LUPM,CNRS,IN2P3) and J. L. Racusin (NASA/GSFC) report on behalf of the Fermi-LAT team: On July 28, 2017, Fermi-LAT detected high-energy emission from GRB 170728B, which triggered the Fermi-GBM (trigger 522975804) at 23:33:32 UT July, 28 2017. This burst was also detected by Swift (Cenko et al., GCN Circ. 21371). The best LAT on-ground location is found to be RA, Dec 238.97, 69.74 (degrees, J2000) with an error radius of 0.53 deg (90% containment, statistical error only). This was 30 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 is spatially and temporally correlated with the GBM emission with high significance. More than 10 photons above 100 MeV are observed within 100 seconds. The highest-energy photon is a 0.6 GeV event which is observed 9.3 seconds after the GBM trigger. The Fermi-LAT point of contact for this burst is Manal Yassine (manal.yassine@lupm.in2p3.fr). 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.