TITLE: GCN CIRCULAR NUMBER: 19843 SUBJECT: GRB 160821B: Fermi GBM Detection DATE: 16/08/22 20:18:16 GMT FROM: Matthew Stanbro at UAH/Fermi M. Stanbro (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 22:29:13.33 UT on 21 August 2016, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 160821B (trigger 493511357 / 160821937), which was also detected by the Swift/BAT (Siegel et al. 2016, GCN 19833) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 61 degrees. The GBM light curve consists of a few episodes with a duration (T90) of about 1 s (50-300 keV). The time-averaged spectrum from T0-0.13 s to T0+0.32 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.37 +/- 0.22 and the cutoff energy, parameterized as Epeak, is 84 +/- 19 keV The event fluence (10-1000 keV) in this time interval is (1.68 +/- 0.19)E-06 erg/cm^2. The 64-millisec peak photon flux measured starting from T0+0.00 s in the 10-1000 keV band is 9.16 +/- 1.19 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."