TITLE: GCN CIRCULAR NUMBER: 30065 SUBJECT: GRB 210520A: Fermi GBM detection DATE: 21/05/21 12:41:47 GMT FROM: Peter Veres at UAH P. Veres, B. Hristov and C. Meegan (all UAH) report on behalf of the Fermi GBM Team: "At 19:07:02.00 UT on 20 May 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 210520A (trigger 643230427 / 210520797) which was also detected by the Fermi LAT (Di Lalla et al., GCN 30062) and GECAM (Zheng et al GCN 30061). The GBM on-ground location (reported in GCN 30059) is consistent with the LAT position. The angle from the Fermi LAT boresight at the GBM trigger time is 21 degrees. The GBM light curve consists of a large number of pulses with a duration (T90) of about 56 s (50-300 keV). The time-averaged spectrum from T0-1.3 s to T0+58 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -1.18 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 4.4 +/- 1.8 MeV. The event fluence (10-1000 keV) in this time interval is (1.02 +/- 0.04)E-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 2.6 +/- 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/"