GCN Circular 22277
M. Stanbro (UAH), C. M. Hui (NASA/MSFC) and C. Meegan (UAH) reports on behalf of the Fermi GBM Team: At 16:25:10.54 UT on 22 December 2017, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 171222A (trigger 535652715/171222684) which was also detected by the Swift/BAT and XRT (Racusin et al. 2017, GCN 22265). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 43 degrees. The GBM light curve shows a single peak with a duration (T90) of about 80.4s (50-300 keV). The time-averaged spectrum from T0+0.0s to T0+78.8s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.09+/- 0.27 and the cutoff energy, parameterized as Epeak, is 29.18 +/- 2.73 keV. The event fluence (10-1000 keV) in this time interval is (2.27 +/- 0.13)E-06 erg/cm^2. The 1s peak photon flux measured starting from T0+60.1s in the 10-1000 keV band is 2.3 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog.