TITLE: GCN CIRCULAR NUMBER: 28748 SUBJECT: GRB 201021C: Fermi GBM detection DATE: 20/10/22 15:41:24 GMT FROM: Stephen Lesage at Fermi-GBM Team S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 20:27:21.92 UT on 21 October 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 201021C (trigger 625004846 / 201021852) which was also detected by the Swift/BAT (A. Y. Lien et al. 2020, GCN 28730). The Fermi GBM on-ground localization is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is ~59 degrees. The GBM light curve shows a single bright peak with a duration (T90) of about 35.3 s (50-300 keV). The time-averaged spectrum from T0-5.9 s to T0+29.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 131.1 +/- 28.2 keV. The event fluence (10-1000 keV) in this time interval is (1.7 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0-1.9 s in the 10-1000 keV band is 1.82 +/- 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/"