TITLE: GCN CIRCULAR NUMBER: 33125 SUBJECT: GRB 221226A: Fermi GBM detection DATE: 22/12/30 16:17:59 GMT FROM: Peter Veres at UAH P. Veres and C. Meegan (both UAH) report on behalf of the Fermi GBM Team: "At 16:44:27.06 UT on 26 December 2022, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 221226A (trigger 693765872 / 221226698) which was also detected by the AGILE (Panebianco et al., GCN 33113) and Swift/BAT (Raman et al., GCN 33121). The Fermi GBM Final Real-time Localization was reported in GCN 33104, and it is consistent with the IPN triangulation (Kozyrev et al., GCN 33123) The GBM light curve consists of two emission episodes with a duration (T90) of about 129 s (50-300 keV). The time-averaged spectrum from T0-3 s to T0+129 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.18 +/- 0.03 and the cutoff energy, parameterized as Epeak, is 340 +/- 32 keV. The event fluence (10-1000 keV) in this time interval is (2.98 +/- 0.10)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.8 s in the 10-1000 keV band is 20.7 +/- 0.4 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 229 +/- 35 keV, alpha = -1.10 +/- 0.05 and beta = -1.90 +/- 0.08. 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/"