TITLE: GCN CIRCULAR NUMBER: 20986 SUBJECT: GRB 170405A: Fermi GBM observation DATE: 17/04/05 22:51:57 GMT FROM: C. Michelle Hui at MSFC/Fermi-GBM C. M. Hui (MSFC) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: At 18:39:22.89 UT on 05 April 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170405A (trigger 513110367/170405777), which was also detected by Swift (Troja et al. 2017, GCN 20984). The GBM on-ground location is consistent with the Swift position. The trigger resulted in an Autonomous Repoint Request (ARR) by the GBM Flight Software owing to the high peak flux of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight location. The initial angle from the Fermi LAT boresight is 52 degrees. The GBM light curve shows multiple peaks with a duration (T90) of about 78.6 s (50-300 keV). The time-averaged spectrum from T0+7.2 s to T0+86.0 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.01 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 355.2 +/- 8.6 keV. The event fluence (10-1000 keV) in this time interval is (7.85 +/- 0.07)E-05 erg/cm^2. The 1s peak photon flux measured starting from T0+29.5 s in the 10-1000 keV band is 15.8 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.