TITLE: GCN CIRCULAR NUMBER: 21157 SUBJECT: GRB 170527A: Fermi GBM detection DATE: 17/05/27 20:09:57 GMT FROM: C. Michelle Hui at MSFC/Fermi-GBM M. Stanbro (UAH), C. M. Hui (NASA/MSFC), C. Meegan (UAH) and A. von Kienlin (MPE) report on behalf of the Fermi GBM Team: At 11:31:02.37 UT on 27 May 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170527A (trigger 517577467 / 170527480). The on-ground calculated location, using the GBM trigger data, is RA = 195.19 , DEC = +0.94 (J2000 degrees, equivalent to 13h 00m, +0d 54.0'), with an uncertainty of 1.00 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 is 37.00 degrees. The GBM light curve shows a sharp peak with multiple sub-structures with a duration (T90) of about 49.2 s (50-300 keV). The time-averaged spectrum from T0+1.1 s to T0+50.3 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.03 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 1001.00 +/- 33.50 keV The event fluence (10-1000 keV) in this time interval is (8.430 +/- 0.003)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.8 s in the 10-1000 keV band is 22.19 +/- 0.36 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.