TITLE: GCN CIRCULAR NUMBER: 20786 SUBJECT: GRB 170228A: Fermi GBM observation DATE: 17/03/01 16:32:05 GMT FROM: Peter Veres at UAH P. Veres, M. Stanbro and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 19:03:00.71 UT on 28 February 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 170228A (trigger 510001385 / 170228794) which was also detected by Fermi/LAT (Bissaldi et al., GCN 20785). The GBM on-ground location is consistent with the LAT position. The GBM light curve shows a single pulse followed by weaker emission with a duration (T90) of about 62 s (50-300 keV). The time-averaged spectrum from T0 to T0 + 18.8 s is best fit by a Band function with Epeak = 755 +/- 76 keV, alpha = -0.50 +/- 0.07, and beta = -2.35 +/- 0.17. The event fluence (10-1000 keV) in this time interval is (2.23 +/- 0.06)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.0 s in the 10-1000 keV band is 10.2 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."