GCN Circular 28326
S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 13:58:14.66 UT on 29 August 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 200829A (trigger 620402299 / 200829582) which was also detected by the Swift Burst Alert Telescope (BAT) (M. H. Siegel et al. 2020, GCN 28307). GBM initially triggered on a weak spike ~15-20 s before the very bright emission. The GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight at the GBM trigger time is ~148 degrees. The GBM light curve shows an exceptionally bright long GRB with a duration (T90) of about 6.9 s (50-300 keV). The time-averaged spectrum from T0+16.64 s to T0+25.856 s is best fit by a Band function with Epeak = 336.8 +/- 4.3 keV, alpha = -0.43 +/- 0.01, and beta = -2.4 +/- 0.02 The event fluence (10-1000 keV) in this time interval is (2.069 +/- 0.009)E-04 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+19.7 s in the 10-1000 keV band is 213.9 +/- 1.7 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/"