GCN Circular 23598
P. Veres, R. Hamburg and C. Meegan (all UAH) report on behalf of the Fermi GBM Team: "At 03:27:43.75 UT on 31 December 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 181231A (trigger 567919668 / 181231144) which was also detected by Fermi/LAT (Dirirsa et al., GCN 23597). The GBM on-ground location is consistent with the LAT position. The GBM light curve shows multiple peaks with a duration (T90) of about 37 s (50-300 keV). The time-averaged spectrum from T0-7.2 s to T0+30.7 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.13 and the cutoff energy, parameterized as Epeak, is 215 +/- 25 keV. The event fluence (10-1000 keV) in this time interval is (6.23 +/- 0.46)E-6 erg/cm^2. The 1 second peak photon flux measured starting from T0+14.3 s in the 10-1000 keV band is 2.70 +/- 0.27 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."