//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21404 SUBJECT: GRB 170802A: Fermi GBM detection DATE: 17/08/03 02:25:02 GMT FROM: Matthew Stanbro at UAH/Fermi M. Stanbro and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 15:18:24.80 UT on 02 August 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170802A (trigger 523379909 / 170802638). The on-ground calculated location, using the GBM trigger data, is RA = 52.3, DEC = -39.2, with an uncertainty of 2.1 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ). 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 to the GBM best location is 41 degrees. The GBM triggered on a precursor that was followed ~1 s later by a brighter peak. The total duration (T90) was about 2 s (50-300 keV). The time-averaged spectrum from T0-0.13 s to T0+2.24 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.80 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 952 +/- 200 keV. The event fluence (10-1000 keV) in this time interval is (2.70 +/- 0.11)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.41 s in the 10-1000 keV band is 8.20 +/- 0.27 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 670 +/- 163 keV, alpha = -0.70 +/- 0.11 and beta = -2.09 +/- 0.25. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."