GCN Circular 27460
C. Malacaria (NASA-MSFC/USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 14:53:16.04 UT on 25 March 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 200325B (trigger 606840801 / 200325620), which was also detected by the Swift/XRT (GCN 27457). The optical counterpart was detected by MASTER (GCN 27446), Mondy (GCN 27452), and LCO (GCN 27457). The angle from the Fermi LAT boresight at the GBM trigger time is 102.5 degrees. The GBM light curve shows a broad peak with several spikes overimposed, with a duration (T90) of about 36.6 s (50-300 keV). The time-averaged spectrum from T0-8.1 s to T0+36.9 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.33 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 150.1 +/- 12.8 keV. The event fluence (10-1000 keV) in this time interval is (1.12 +/- 0.04)e-5 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10.7 s in the 10-1000 keV band is 9.1 +/- 0.3 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/"