GRB 201221D: Fermi GBM detection

"At 23:06:34.33 UT on 21 December 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 201221D (trigger 630284799 / 201221963) which was also detected by the Swift/BAT and Swift/XRT (Page et al. 2020, GCN 29112) and Konus-Wind (Frederiks et al. 2020, GCN 29130). This trigger was initially classified as a particle event by the flight software, but is in fact a GRB. The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 89 degrees. The GBM light curve shows a single-peaked structure with a duration (T90) of about 0.14 s (50-300 keV). The time-averaged spectrum from T0-0.064 s to T0+0.192 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.20 +/- 0.16 and the cutoff energy, parameterized as Epeak, is 108 +/- 5 keV. A Band function fits the spectrum equally well with Epeak = 98 +/- 8 keV, alpha = 0.01 +/- 0.24 and beta = -3.3 +/- 0.5. The event fluence (10-1000 keV) in this time interval is (1.076 +/- 0.046)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.00 s in the 10-1000 keV band is 41 +/- 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/"