TITLE: GCN CIRCULAR NUMBER: 12744 SUBJECT: GRB 111228A: Fermi GBM observation DATE: 11/12/28 23:03:23 GMT FROM: Michael S. Briggs at UAH and MSFC M. S. Briggs (UAH) and G. Younes (USRA) report on behalf of the Fermi GBM Team: "At 15:45:30.80 UT on 28 Dec 2011, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 111228A (trigger 346779932 / 111228657), which was also detected by the Swift BAT/XRT/UVOT (Ukwatta et al. 2011, GCN 12737). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 70 degrees. The GBM light curve shows multiple peaks in three groups with a duration (T90) of about 100 s (50-300 keV) starting 50 seconds before the GBM trigger time. The time-averaged spectrum from T0+0 s to T0+57 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -1.9 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 34 +/- 4 keV A Band function fits the spectrum equally well with Epeak= 34 +/- 3 keV, alpha = -1.9 +/- 0.1 and beta = -2.7 +/- 0.3. The event fluence (10-1000 keV) in this time interval is 1.8E-5 erg/cm^2. The 64 ms peak photon flux measured starting from T0+7.7 s in the 10-1000 keV band is 27 +/- 1 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."