TITLE: GCN CIRCULAR NUMBER: 21406 SUBJECT: GRB 170803A: Fermi GBM observation DATE: 17/08/03 23:03:54 GMT FROM: Peter Veres at UAH P Veres and C Meegan (both UAH) report on behalf of the Fermi GBM Team: "At 17:30:27.112 UT on 3 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170803A (trigger 523474232 / 170803729) which was also detected by the Swift/BAT (LaPorte et al., GCN 21405). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 40 degrees. The GBM light curve consists of a single pulse with a duration (T90) of about 3.6 s (50-300 keV). The time-averaged spectrum from T0-0.1 s to T0+2.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.71 +/- 0.12 and the cutoff energy, parameterized as Epeak, is 154 +/- 13 keV. The event fluence (10-1000 keV) in this time interval is (1.65 +/- 0.076)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.1 s in the 10-1000 keV band is 9.1 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."