TITLE: GCN CIRCULAR NUMBER: 29637 SUBJECT: GRB 210306B: Fermi GBM detection DATE: 21/03/09 17:13:46 GMT FROM: Stephen Lesage at Fermi-GBM Team S. Lesage (UAH), A. von Kienlin (MPE), and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 09:32:14.42 UT on 06 March 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210306B (trigger 636715939 / 210306397) which was also detected by the Swift/BAT (Ambrosi et al. 2021, GCN 29601). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 37 degrees. The GBM light curve shows a single-peaked structure with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum from T0-1.3 s to T0+14.1 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.0 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 73 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (1.3 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.0 s in the 10-1000 keV band is 2.7 +/- 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/"