TITLE: GCN CIRCULAR NUMBER: 33112 SUBJECT: GRB 221226B: Fermi GBM Observation DATE: 22/12/27 13:16:51 GMT FROM: Rachel Hamburg at UAH S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 22:41:20 UT on 26 December 2022, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 221226B (trigger 693787285/221226945), which was also detected by Swift BAT (S. B. Cenko et al. 2022, GCN 33108) and has a measured redshift from the VLT/X-Shooter (GCN 33110). The Fermi GBM Final Real-time Localization (GCN 33107) is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 58 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+0.002 to T0+2.592 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is 0.2 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 104 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (7.8 +/- 0.5)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.3 s in the 10-1000 keV band is 4.1 +/- 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/"