GCN Circular 33146
S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 21:46:05 UT on 31 December 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221231A (trigger 694215970/221231907). which was also detected by Swift BAT (A. Tohuvavohu et al. 2023, GCN 33132) and Swift XRT GCN (M. Perri et al. 2023, 33139). The Fermi GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 61 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 5 s (50-300 keV). The time-averaged spectrum from T0-0.06 to T0+4.93 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.2 +/- 0.4 and the cutoff energy, parameterized as Epeak, is 200 +/- 40 keV. The event fluence (10-1000 keV) in this time interval is (4.4 +/- 0.4)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0 s in the 10-1000 keV band is 3.9 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"